This manual is for C-INTERCAL version 0.29. It does not replace the old groff manual, nor is it designed to be read in conjunction with it; instead, it serves a different purpose, of providing information useful to users of C-INTERCAL (unlike the other manual, it is not derived from the original INTERCAL-72 manual).
Copyright © 2007 Alex Smith.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free Documentation License.”
This is the Revamped Instruction Manual for C-INTERCAL (this version is distributed with C-INTERCAL version 0.29). It is divided into four parts.
The first part is about the C-INTERCAL compiler
ick, and how to use it. It covers installing the compiler,
using the compiler, what error and warning messages are produced by the
compiler, and some information on how to use the debugger.
The second part is about the core INTERCAL language, invented in 1972, and some other commands since then which don’t feel like they’re extensions. (This is a pretty arbitrary distinction, but people who write the documentation are entitled to arbitrary distinctions. The manual’s licensed under a license that lets you change it (see Copying), so if you disagree you can move the commands from section to section yourself.) Mostly only commands that are implemented in C-INTERCAL are covered here (if you’re interested in the other commands implemented in other compilers, read CLC-INTERCAL’s documentation). However, a comprehensive guide to portability of these commands between C-INTERCAL and other INTERCAL compilers is given.
The third part covers the INTERCAL extensions and dialects that are implemented by C-INTERCAL, such as TriINTERCAL and Threaded INTERCAL. Again, extensions and dialects not implemented have been mostly left out.
The final part contains appendices (which were known as
‘tonsils’ in the original INTERCAL
manual), such as character sets used by INTERCAL,
programs other than ick in the C-INTERCAL
distribution, information on how to read and update the list of
optimizer idioms used by the compiler, and the copyright.
The C-INTERCAL distribution is distributed in source code form; this means that before using it, you first have to compile it. Don’t worry: if you have the right software, it’s not at all difficult. Most Linux-based and UNIX-based computers are likely to have the software needed already; the software needed to compile source-distributed packages is also readily available for free for other operating systems. The following instructions will help you install the distribution in a method appropriate for your system.
C-INTERCAL distributions have been stored in many different places over time; it can sometimes be hard to make sure that you are finding the most recent version. In order to make sure that you have the most recent version, the easiest way is to look at the alt.lang.intercal newsgroup; all releases of the C-INTERCAL compiler ought to be announced there. (If you are interested in what other INTERCAL compilers are available, it may also be worth looking there.) If you don’t have access to a newsreader, your newsreader doesn’t cover that newsgroup, or the distance between releases has been too large for your news server to keep the message, it’s likely that you can find the announcement in an archive on the World Wide Web; at the time of writing (2007), the archives of the newsgroup are stored by Google Groups, and a search for ‘alt.lang.intercal’ there should tell you where to find a copy.
If you’re looking for the latest version, note that the number after the dot represents the major version number; you want to maximise this in favour of the number before the dot, which is the bugfix level within a major version. (Major versions are released as version 0.whatever; if a new version comes out that fixes bugs but adds no new features, nowadays its number will be of the form 1.whatever, with the same major number. This has not always been the case, though.)
C-INTERCAL is distributed in compressed pax format; for
instance, you may find it as a ‘.pax.lzma’
file if you have the unlzma decompression program (this is
advised, as it’s the smallest);
‘.pax.bz2’ is larger and
‘.pax.gz’ is larger still. Most computers can
decompress files in this format, even if they don’t realise it,
because pax is forwards-compatible with tar; try renaming the extension
from ‘.pax’ to ‘.tar’
after decompressing to see if you have a progam that can decompress it.
(If you’re wondering why such an apparently non-standard format
is being used, this is is actually a case where C-INTERCAL
is being perfectly nonstandard by conforming to the standards; tar is
no longer specified by POSIX, and pax is its replacement. It’s
just that pax never really caught on.)
It doesn’t matter where you extract the distribution file to: it’s best if you don’t put it anywhere special. If you aren’t an administrator, you should extract the file to somewhere in your home directory (Linux or UNIX-like systems) or to your My Documents directory (recent versions of Windows; if you’re using an older version, then you are an administrator, or at least have the same privileges, and can extract it anywhere). Some commands that you might use to extract it:
unlzma ick-0-29.pax.lzma tar xvf ick-0-29.pax
or
bunzip2 ick-0-29.pax.bz2 tar xvf ick-0-29.pax
or
gunzip ick-0-29.pax.gz tar xvf ick-0-29.pax
On most UNIX-based and Linux-based systems, tar will
be available to unpack the installation files once they’ve
been uncompressed with gunzip. (I’ve heard that
some BSD systems have pax itself to decompress the
files, although have not been able to verify this; some Linux
distributions also have pax in their package managers.
Both tar and pax should work fine, though.) gunzip is
also likely to be available (and bunzip2 and
unlzma are less likely, but use those versions if you
have them to save on your bandwidth); if it isn’t, you will
need to download a copy from the Internet.
tar xzvf ick-0-29.pax.gz
or
tar xqvf ick-0-29.pax.bz2
If you are using the GNU version of tar (which is very
likely on Linux), you can combine the two steps into one as shown
here, except when using the lzma-compressed version.
djtar -x ick-0-29.pax.gz
On a DOS system, you will have to install DJGPP anyway to be able
to compile the distribution, and once you’ve done that you
will be able to use DJGPP’s decompressing and unpacking
utility to extract the files needed to install the distribution.
(You will need to type this at the command line; on Windows 95 and
later, try choosing Run... from the start menu then typing
cmd (or command if that fails) in the
dialog box that opens to get a command prompt, which you can exit
by typing exit. After typing any command at a command
line, press RET to tell the shell to execute
that command.)
If you’re running a Windows system, you could always try double-clicking on the ick-0-29.pax.gz file; probably renaming it to have the extension ‘.tgz’ is likely to give the best results. It’s quite possible that you’ll have a program installed that’s capable of decompressing and unpacking it. Unfortunately, I can’t guess what program that might be, so I can’t give you any instructions for using it.
Whatever method you use, you should end up with a directory created
called ick-0.29; this is your main installation directory
where all the processing done by the installation will be carried out.
You will need to have that directory as the current directory during
install (at the command prompt in all the operating systems I know, you
can set the current directory by typing cd ick-0.29).
There are scripts included in the distribution to automate the process of installing, in various ways. The simplest method of installing on most operating systems (on DOS, see Installation on DOS) is to use the following routine:
configure. Although building in the distribution directory
works, it is recommended that you build elsewhere; create a directory
to build in (using mkdir on most operating systems), then
run configure from inside that directory (for instance,
you could do this from inside the main installation directory:
mkdir build cd build ../configure
to build in a subdirectory of the distribution called
“build”). You also specify where you want the files to
be installed at this stage; the default of
‘/usr/local’ is good for many people, but
you may want to install elsewhere (in particular, if you want to
test out C-INTERCAL without installing it, create a
new directory somewhere you own and specify that as the place to
install it, so the install will actually just copy the files into
the right structure for use instead of installing them). To specify
a location, give the option
--prefix=location to configure; for
instance, configure --prefix=/usr would install in
/usr.
make. The
Makefile will be set up for your version of make, and to
automatically recompile only what needs compiling (it will even
recompile the build system if you change that).
make install. (This is the only step that needs
root/administrator permissions; so on a system that uses sudo to
elevate permissions, for instance, write it as sudo make
install if you’re installing into a directory that you
can’t write to as a non-administrative user.) This step is
optional; if you do not install C-INTERCAL, you can still
run it by directly referencing the exact location of the
ick command.
On all systems, it’s worth just trying this to see if it works.
This requires a lot of software on your computer to work, but all of it
is standard on Linux and UNIX systems. The first command is a
shell-script which will analyse your system and set settings
accordingly; it will explain what it’s doing and what settings it
detected, and create several files in the installation directory to
record its results. (This is a configure script produced by the GNU
autoconf (configure); its autoconf source code is available in the file
configure.ac.) The second command actually compiles the
source code to produce binaries; this takes the longest of any of the
steps. You will see all the commands that it’s running as it runs
them. The third command will copy the files it’s compiled to
appropriate shared locations on your system so that anyone on the
system can just use ick.
There may be various factors that prevent this simple installation
method working. On a system not based on UNIX or Linux, you may find
that you don’t have some of the software required to run this
(for instance, you may be missing the shell sh, and
don’t have the shell bash which can emulate it, and
so can’t run configure that depends on one of those
shells being available) and so this method won’t work for you. In
such cases, one solution may be to install all the software required;
the GNU project has a version of all the commands required, for
instance, and there may be ports available for your operating system.
However, the only software absolutely required is a C compiler
(C-INTERCAL was designed to work with gcc and
is tested mostly with that compiler, but in theory it should work with
other C compilers too, and this is tested on occasion) and the
associated software needed to compile C files to object files and
executables, combine object files into libraries, etc.; but this
requires trying to do the build by hand, so it’s generally easier
just to install a UNIX-like shell and associated tools.
Another possibility that might stop this process working is if your
version of the relevant software is incompatible with the GNU versions
that were used for testing. For instance, I have come across
proprietary versions of lex that need directives in the
source file to say in advance how much memory the lexer-generator needs
to allocate. In such cases, pay attention to the error messages
you’re getting; normally they will suggest trivial modifications
to the source files that will cause the compilation to work again.
Some Linux and UNIX systems (notably Debian and Ubuntu) don’t have the required files for compilation installed by default. To install them, just download and install the required packages: for Ubuntu at the time of writing, they are ‘binutils’, ‘cpp’, ‘gcc’, ‘libc6-dev’, ‘make’ to compile C-INTERCAL, and if you want to modify it, you may also need ‘autoconf’, ‘automake’, ‘bison’, and ‘flex’. For debugging help, you may also want ‘gdb’, and to recompile the documentation, you may need ‘groff’, ‘texlive’, ‘texinfo’, and ‘tidy’.
If you’re trying to do something unusual, you probably want to
set some of the settings yourself rather than letting the compilation
process guess everything. In this case, use configure
--help to view the options that you can set on
configure; there’s a wide range of settings that you
can set available there, and one of them may be what you want.
On DOS-based systems, it’s possible to install C-INTERCAL via compiling it using DJGPP, a free DOS development system. (You can obtain DJGPP via its homepage, at http://www.delorie.com/djgpp/.) The process for installing it works like this:
You might want to install other packages, particularly GNU Bison and GNU Flex, in order to be able to rebuild certain parts of the compiler if you change them. This is not necessary to simply be able to run C-INTERCAL without changing it, though.
bash session, change to the
‘buildaux’ subdirectory of your main
C-INTERCAL directory, and run the command
build-dj.sh. This will run the entire
C-INTERCAL build system, and hopefully end up with
executables you can run in the ‘build’
subdirectory that will be created in your main C-INTERCAL
directory.
make install from the new
‘build’ subdirectory. It will run just fine
in-place without a need to install, though, if you prefer.
It may happen that you decide to uninstall C-INTERCAL after installing it; this may be useful if you want to test the installation system, or change the location you install programs, or for some reason you don’t want it on your computer. It’s worth uninstalling just before you install a new version of C-INTERCAL because this will save some disk space; you cannot install two versions of C-INTERCAL at once (at least, not in the same directory; but you can change the --prefix of one of the installations to get two versions at once).
If you installed C-INTERCAL using make
install, you can uninstall it by using make
uninstall from the installation directory, assuming that it
still exists. If you can’t use that method for some reason, you
can uninstall it by deleting the files ick and
convickt where your computer installs binaries (with an
extension like ‘.exe’ added if that’s
usual for binaries on your operating system), libick.a,
libickmt.a, libickec.a, and
libyuk.a where your computer installs libraries, and the
subdirectories ick-0.29 in the places where your computer
installs data files and include files, and their contents.
You can go further than uninstalling. Running make clean
will delete any files created by compilation; make
distclean will delete those files, and also any files created by
configuring. It’s probably a wise idea to uninstall before doing
a distclean, though, as otherwise information needed to uninstall will
be deleted, as that information is generated by configure.
You can go even further and use make veryclean which will
delete not only files created by configuring, but the entire build
system; doing so is not recommended unless you have some method of
rebuilding the build system from its original sources (a script to do
this is provided in repository versions of C-INTERCAL,
because the generated part of the build system is not stored in the
repository).
If you can’t get C-INTERCAL to install at all, or something goes wrong when you’re using it, reporting a bug is probably a good idea. (This is still important even if you figure out how to fix it, and the information isn’t in the manual, because the fix can be added to the source code if possible, or at least to the manual, to benefit future users.) For general help, you may want to post to the alt.lang.intercal news group; to report a bug or submit a patch, email the person who released the most recent C-INTERCAL version (which you can determine by looking at that newsgroup).
If you do find a bug (either the compiler not behaving in the way you’d expect, or if you find a way to cause E778 (see E778) without modifying the source code), it helps a lot if you can submit a bug report explaining what causes it. If you’re not sure, say that; it helps if you give examples of input, command line options, etc. that cause the bug. There are several debug options (see Debug Options) that you can use to help pin down a bug if you’re interested in trying to solve the problem yourself; looking at the output C code can also help pin down a bug if the compiler gets that far.
Information that should be given in a bug report is what you expect to
happen, what actually happens, what input and command line options you
gave to the compiler, what operating system you’re using, any
ideas you might have as to what the problem is, and any appropriate
debug traces (for instance, -H (see -H) output if you think the bug is in the
optimizer). Core dumps aren’t portable between systems, so
don’t send those; however, if you’re getting an internal
error and can dump core with -U (see -U), it helps if you can load a debugger (such as
gdb) on the core dump, use the debugger to produce a
backtrace, and send that backtrace.
If you figure out how to solve the bug yourself, and want to submit the
patches to help other users (this also carries the advantage that your
patches will then be maintained along with the rest of the
distribution, and that you won’t have to reapply them every time
you upgrade to a newer version of C-INTERCAL), you must
first agree to license your code under the same license as the code
that surrounds it (normally, that’s the GNU General Public
License, but if you submit a patch to a file with a different license,
like this manual (yes, documentation patches are useful too), you must
agree to that license). You will be credited for the patch in the
source code unless you specifically ask not to be or you don’t
give your name (in both these cases, you must license the code to the
public domain so that it can be incorporated without the attribution
requirement). Preferably, patches should be submitted in the format
created by the command diff -u; this command is likely to
be available on UNIX and Linux systems and versions are also available
for DOS and Windows (including a DJGPP port of the GNU version). If you
can’t manage that, just submit your new code with enough lines of
old code around it to show where it’s meant to go, and a
description of approximately where in the file it was. Patches should
be submitted by email to the person who most recently released a
version of C-INTERCAL.
If you have a suggestion for a new feature, it makes sense to first discuss it on the alt.lang.intercal news group; other INTERCAL compiler maintainers may also want to implement that feature. If you have developed code to implement that feature in C-INTERCAL, you can submit it the same way that you would submit a patch for a bug.
Due to the licensing conditions of C-INTERCAL, you are allowed to release your own version or distribution if you want to. In such cases, it’s recommended that you follow the following guidelines:
make distcheck, which will make the distribution
paxballs, and rename them to have the correct extensions (Automake
thinks they’re tarballs, so will use
‘.tar’ rather than
‘.pax’, and you have to fix this by hand).
make distcheck will also perform some sanity checks on the
build system of the resulting paxball, which will help to ensure that
nothing important is missing from it; and some regression tests on a
version of C-INTERCAL built from the distribution tarball itself, to
prove that it runs correctly and produces plausible output. (A failure
of the regression checks will not stop the build, but should stop you
distributing the resulting compiler.)
All operations on INTERCAL source code available in
C-INTERCAL, other than the conversion from one character
set to another, are currently carried out by the compiler
ick.
The syntax is
ick -options inputfile
(Options can be given preceded by separate hyphens, or all in a row after one hyphen, or a mixture; they’re all single characters.) By default, this compiles one INTERCAL program given as the input file directly to an executable without doing anything fancy; usually you will want to give options, which are described below.
The following command-line options to ick affect what
dialect of the INTERCAL language is compiled by the
compiler; you may need to set one or more of these options if your
input is not the default C-INTERCAL but instead some other
language like INTERCAL-72 or CLC-INTERCAL, or
just because you like certainty or like being different with respect to
your output. Note that there is no command-line option corresponding to
TriINTERCAL (or the base 4-7 versions); instead, the
numeric base to use is determined by looking at the filename extension
(‘.i’ for base 2, the default, or
‘.3i’ to ‘.7i’ for
the base 3-7 versions.)
If this option is not given, there is a small chance that a random bug appears in the compiler, which causes the programs it creates to manifest a bug that causes error E774 (see E774). Giving the option means that this bug will not happen. (You may wonder why this bug was preserved; it is in fact a bug that was carefully preserved since the days of INTERCAL-72, in this case, but the option to turn it off is available as a workaround. (There are no plans to fix this or any of the other carefully preserved bugs any time soon, because that would kind of defeat the point of having preserved them.) Interestingly, the INTERCAL-72 compiler documentation mentions a similar command-line option that is a workaround for the same bug.)
This option needs to be given to allow any multithreading or backtracking commands or identifiers to be used. (Unlike with other language features, this is not autodetected because it’s legal to have a program with multiple COME FROM (see COME FROM) commands aiming at the same line even when it isn’t multithreaded, in which case the commands cause error E555 (see E555) when that line is encountered (with the usual caveats about both commands having to be active at the time).) Attempts to use non-COME FROM multithreading or backtracking commands without this option produce error E405 (see E405).
This option makes it possible to link non-INTERCAL programs with INTERCAL programs; instead of giving INTERCAL programs only on the command line, give one INTERCAL program, followed by any number of programs in other languages that have been written to be able to link to INTERCAL programs. It also allows expansion libraries to be specified on the command line, after the INTERCAL program (expansion libraries are given with no extension). For more information, see External Calls. Also, both the -a and -e options must be set to use CREATEd operators (regardless of whether external calls are used or not).
This option causes the system library to never be linked; this option is only useful if your program references a line number in the range 1000 to 1999, contains no line numbers in that range, and yet still doesn’t want the system library to be linked in; therefore, it is mostly useful with -e when adding in a custom replacement system library written in a non-INTERCAL language, especially the expansion library syslibc (a system library replacement written in C).
This option tells the compiler to treat the source code as INTERCAL-72; as a result, any language constructs that are used but weren’t available in 1972 will trigger error E111 (see E111).
This option allows the CREATE statement (see CREATE) to be used. Note that enabling it carries a run-time penalty, as it means that operand overloading code has to be generated for every variable in the program. (This option is not necessarily needed for the external call version of CREATE to work, but the external call version has fewer features without it.) Note that -e (see -e) also needs to be set to be able to CREATE operators.
It is possible to write INTERCAL code
sufficiently tortuous that it ends up assigning to a constant.
Generally speaking, this isn’t what you wanted to do, so the
compiler will kindly cause an error (E277; see E277) that stops the insanity at that point, but at the
cost of a significant amount of performance you can give this
option to tell the compiler to simply change the constant and keep
on going anyway. (Note that unlike CLC-INTERCAL, this
only changes uses of the constant preceded by # in
your program, not things like line numbers; you want Forte for that.) This option
also allows you to write arbitary expressions on the left of an
assignment statement if you wish.
When this option is given, the generated programs will write the number 4 as ‘IIII’ rather than ‘IV’, in case you’re writing a clock program.
This tells the compiler to treat the input as PIC-INTERCAL (see PIC-INTERCAL) rather than ordinary C-INTERCAL input, and generate PIC output code accordingly. There are a lot of options that are incompatible with this, as well as many language features, due to the limited memory available on a PIC. If you get error E256 (see E256), you have this option given when it shouldn’t be; likewise, if you get error E652 (see E652), you should be using this option but aren’t. (A few simple programs are C-INTERCAL/PIC-INTERCAL polyglots, but such programs are incapable of doing input or output, meaning that they aren’t particularly useful.)
The C-INTERCAL and CLC-INTERCAL compilers
use different notation for various things, sometimes to the extent
where the same notation is legal in both cases but has a different
meaning. As this is the C-INTERCAL compiler, it rather
guessably uses its own notation by default; however, the
CLC-INTERCAL notation can be used as the default
instead using this option. (In most situations where there
isn’t an ambiguity about what something means, you can use
the ‘wrong’ syntax freely.) The option causes ambiguous
characters like ? to be interpreted with Princeton
rather than Atari meanings.
This option causes some constructs with different meanings in C-INTERCAL and CLC-INTERCAL to use the CLC-INTERCAL meaning rather than the C-INTERCAL meaning. At present, it affects the abstention of a GIVE UP (see GIVE UP) command by line number, which is possible as long as this switch isn’t given; reading through the INTERCAL-72 manual, there are a lot of things that imply that this probably wasn’t intended to be possible, but as far as I can tell that manual doesn’t actually say anywhere that this particular case is disallowed, even though it rules out all other similar cases. It also causes I/O on array variables to be done in CLC-INTERCAL’s extended Baudot syntax, rather than using the Turing Tape method.
Sometimes things will go wrong with your program, or with the way
ick was installed. There may even be unknown bugs in
ick itself (if you find one of these, please report it).
The following options are used to debug the whole system on various
levels.
If you think that something has gone wrong with the parser, or you want to see how your program is being parsed, you can give this option on the command line. All the debug output produced by the parser and lexical analyser will be output.
This option allows debugging of the final executable at the C code level. Any C code generated will be left in place, and the -g option will be given to the C compiler that’s used to compile the code, so all the information needed for a C debugger to be used on the executable will be present there.
These options allow debugging of the optimiser, or produce output helpful for understanding how your program has been summarised. -h produces a summary of what optimiser rules were used, the initial expression and what it was optimised to; -H produces a more expanded view that shows each intermediate step of optimisation, and -hH shows the same output as -H, but written completely using C syntax (the other options output in a strange mix of INTERCAL and C).
This option turns on generation of warnings (see Warnings). To make sure that they aren’t actually useful, or are only marginally useful, the warning generator is far too sensitive, and there is no way to decide which warnings are given and which ones aren’t; you either get all of them or none.
This option causes the program to run immediately after being
compiled, and profiles the resulting program to identify
performance bottlenecks, etc. The usefulness of this depends on the
resolution of the timers on the computer and operating system; DOS,
in particular, is really bad with timer resolution. The output will
be saved in a file called yuk.out when the program
finishes running. It’s legal to turn on both the profiler and
the interactive debugger at the same time, but if you do this the
profiler will also identify bottlenecks in the person typing in
commands to step through the program! The profiler will, in fact,
identify all the timings that particular commands in the program
take; so WRITE IN instructions will often show up as
taking a long time due to their need to wait for input.
This option causes the produced program to support the printflow option fully; when this option is not given, printflow will in most cases have partial or no support (except in multithreaded programs, where this option is redundant), because not all the code needed for it will be included in the program to save space.
When you are getting problems with finding files – for instance, the compiler can’t find the skeleton file (see E999) or the system library (see E127) – this option will let you know, on standard error, where the compiler is looking for files. This may hopefully help you pin down where the file-finding problems are coming from, and also offers the option of simply placing copies of the files where the compiler is looking as a last resort.
This is the main debugging option: it loads yuk, an interactive INTERCAL debugger with ability to step through the program, set breakpoints, view and modify variables, etc. See yuk.
This options causes the command line to be displayed for all calls
to other programs that ick makes (mostly to
gcc); it is therefore useful for debugging problems
with the command lines used when using the external calls system
(see External Calls).
The internal error E778 (see E778) should never
happen. However, there are all sorts of potential problems that may
come up, and if part of the code detects something impossible, or
more usually when the operating system detects things have got too
insane and segfaults, normally this error will just be generated
and that’s that. (I most often get this when I’ve been
writing a new section of code and have made a mistake; hopefully,
all or at least most of these errors are fixed before release,
though.) If you want more information as to what’s going on,
you can give the -U option, which will cause the
compiler to raise an abort signal when an internal error happens.
This can generally be caught by a debugger that’s being run
on ick itself at the time; on many systems, it will
also cause a core dump.
These options allow you to control how far to compile (all the way to an executable, or only to C, etc.), and where the output will be created. Note that the output options may change depending on the other options selected; for instance, many of the debug options will prevent the code being compiled all the way to an executable.
By default, the original INTERCAL code will be compiled all the way to an executable, and the intermediate C and object files produced will be deleted. Giving this option causes the compiler to stop when it has finished producing the C file, leaving the C file there as the final output of the compiler. (Its filename is the same as the source file, but with ‘.c’ as its extension/suffix rather than the source file’s extension.) Without this option, an executable will be produced with the extension changed to whatever’s appropriate for the system you are on (or omitted entirely if that’s appropriate for the system).
This option also places verbose comments in the output C file.
This option causes the compiler to progress no further than
producing the C output file, but instead of writing it to a file
writes it directly to standard output. This might occasionally be
useful when using ick as part of a pipe; it can also
be useful to see how far the compiler gets with compiling code
before an error happens, when you’re trying to track down an
error.
There are various command line options that can be used to tell
ick whether and in what ways to optimize code.
This option requests the compiler to attempt to analyse the flow of
the program and optimize accordingly; for instance, it will detect
which commands can’t possibly be ABSTAINED from
and refrain from generating code to check the abstention status of
those commands.
This option tells the compiler to optimize the output for speed. This is done to crazy extremes; the compiler may take several hours/days analysing the program in some cases and still not come up with an improvement. It turns on all the other optimizer options. Note that not all systems accept this option, because it sometimes outputs a shell script disguised as an executable rather than an actual executable.
This option tells the compiler to apply optimizer idioms to the expressions in the code given, when appropriate. The list of idioms is stored in the file src/idiotism.oil; note that it is compiled into the compiler, though, so you will have to rebuild and reinstall the compiler if you change it. For more information about changing the list of idioms, see Optimizer Idiom Language.
Some options just can’t be classified.
If this option is given, the compiler doesn’t run at all, but instead prints a set of instructions for using it, explaining which options are available on the system you’re on and which options conflict with which other options.
Once the compiler runs and produces an output executable, that executable itself will accept a range of options that control the way it runs. None of these options have to be used; a default value will be assumed if they aren’t.
Whether ‘+’ or ‘-’ is given at the start of this option, it will cause the program to print out what options are available and what state they are in. It will then cause the program to exit via an internal error.
If the ‘+’ version of this is given (rather than the default ‘-’), then the program will print a message explaining that you are a wimp (the mode itself is known as wimpmode), and for the rest of execution will input in Arabic numerals (‘123’ rather than ‘ONE TWO THREE’) and likewise will output in Arabic numerals rather than Roman numerals (such as ‘CXXIII’). True INTERCAL programmers should rarely have to use this mode.
This option does not actually appear to do anything.
This option causes standard output to be flushed whenever any characters are output when the ‘+’ version is used, rather than on each newline (the default ‘-’ version). It is most useful for more responsive pipes when outputting binary data, and also useful for debugging very slow programs.
The usual debugging methods don’t work with multithreaded or backtracking programs. This option exists to give at least a slim chance of working out what is going on with them. It causes the program to print the line number of the command it thinks it may be executing next (i.e. the line number that would be printed if that line had an error) immediately after executing each command, and also an internal identifier for the thread that that command was in. It also prints a trace of what parts of the multithreader are being activated; so for instance, it will tell you when a thread is being forked into multiple threads or when a choicepoint has been deleted. Note that the -w option (see -w) must be given to gain full support for flow printing in non-multithreaded non-backtracking programs, because otherwise the required code to print this information will not be generated.
This option is occasionally capable of doing something, but is deliberately undocumented. Normally changing it will have no effect, but changing it is not recommended.
Various environment variables can be set to affect the operation of
ick.
| Variable | Meaning |
|---|---|
|
ICKINCLUDEDIR
ICKLIBDIR ICKSYSDIR ICKCSKELDIR |
These four environment variables suggest locations in which
ick should look to find various files that it needs:
the skeleton file, system library, C header files and libraries
that it needs, constant-output optimiser, and the GNU General
Public License (which the debugger needs to be able to display on
demand for legal reasons).
|
| CC |
The name of a C compiler to use (defaults to gcc;
C-INTERCAL has recently been tested only with
gcc and clang). This option has no effect
on DJGPP, where gcc is always used.
|
|
ICKTEMP
TMPDIR TEMP TMP |
On DJGPP, ick creates temporary files to pass options
to gcc as a method of getting around the limit on the length of a
command line that can sometimes affect DOS programs. These four
environment variables are tried (in this order) to determine a
location for the temporary file; if none of them are set, the
current directory is used.
|
Things may go wrong, either during the compilation or the execution of your program. Note that some things that would be compile-time errors in many other languages – such as syntax errors – are in fact run-time errors in INTERCAL.
Errors and warnings appear as an error code starting with
‘ICL’, followed by a three digit number,
followed by ‘I’ for an error or
‘W’ for a warning. However, they will be
notated here as ‘E000’, etc., to save space
and because consistency was never a strong point of
INTERCAL. This is followed by a text description of
the error, and a hint as to the location of the error. This is not the
line on which the error occurred, but rather the line on which the next
command to be executed is. To add to the fun, the calculation of the
next command to be executed is done at compile-time rather than
runtime, so it may be completely wrong due to things like abstention on
COME FROMs or computed COME FROMs. The moral
of this story is that, if you really want to know where the error is,
use a debugger. Note also that if the error happens at compile-time,
there is no guarantee that the line number given makes any sense at
all. Some errors don’t give next line numbers, mostly those for
which it doesn’t make logical sense, such as E633 (see E633). After this is a suggestion to correct (or
reconsider) the source code and to resubnit it. (This typo has been
carefully preserved for over a decade.)
This is a list of the error messages that might be produced during the compilation or execution of an INTERCAL program.
This is an unusual error; it’s what’s printed when a
syntax error is encounted at runtime, in a situation in which it
would be executed. (An ABSTAINed syntax error, for
instance, would not be executed; this is one of the mechanisms
available for writing comments.) The text of the error message is
simply the statement that couldn’t be decoded.
DO YOU EXPECT ME TO FIGURE THIS OUT?
This error occurs when there is an attempt to use a constant with a value outside the onespot range; it’s a compile-time error.
PROGRAMMER IS INSUFFICIENTLY POLITE
The balance between various statement identifiers is important. If
less than approximately one fifth of the statement identifiers used
are the polite versions containing PLEASE, that causes
this error at compile time.
PROGRAMMER IS OVERLY POLITE
Of course, the same problem can happen in the other direction; this error is caused at compile time if more than about one third of the statement identifiers are the polite form.
COMMUNIST PLOT DETECTED, COMPILER IS SUICIDING
This error happens when you give the -t option (see -t) but you use a language construct that wasn’t available in INTERCAL-72. If this happens, then either there’s a mistake in the program that prevents it being INTERCAL-72 or you shouldn’t be compiling it as INTERCAL-72 in the first place.
PROGRAM HAS DISAPPEARED INTO THE BLACK LAGOON
There is a hard limit of 80 NEXTs at a time; this is
to discourage excessive use of NEXTING for things like
recursion. (Recursive programs are entirely legal; you simply have
to figure out how to do it with computed COME FROM
instead. (For the record, it is possible. (Using lots of nested
brackets when talking about recursion is great (yay!).))) Another
problem with writing the source code that can cause this error is a
failure to properly FORGET the entry on the
NEXT stack created when trying to simulate a goto.
SAYING ’ABRACADABRA’ WITHOUT A MAGIC WAND WON’T DO YOU ANY GOOD
Your program asked to include a system library (by specifying a line number in a magic range without including a line with that number), but due to installation problems the compiler couldn’t find the system library to include. You could try using the -u (see -u) option to see where the compiler’s looking; that may give you an idea of where you need to copy the system library so that the compilation will work. This error happens at compile time and doesn’t give a next command line number.
PROGRAM HAS GOTTEN LOST
This error happens at compile time when the compiler can’t
figure out where a NEXT command is actually aiming
(normally due to a typo in either the line label given or the line
label on the line aimed for). The logic behind this error means
that the next line to be executed is unknown (after all,
that’s the whole point of the error) and is therefore not
given. The -e command-line option (see -e) makes this error into a run-time error,
because it allows NEXT commands to dynamically change
targets at runtime, as well as line labels to dynamically change
values, and thus the error is impossible to detect at compile time.
I WASN’T PLANNING TO GO THERE ANYWAY
This error happens at compile time when an ABSTAIN or
REINSTATE references a non-existent target line. This
generally happens for much the same reasons as E129 (see E129).
YOU MUST LIKE THIS LABEL A LOT!
At present, it’s impossible to have more than one line with
the same line number. That would make NEXT act too
much like COME FROM in reverse to be interesting. This
error happens at compile time. (For inconsistency, it is
possible to have multiple lines with the same number as long as at
most one of them is in an INTERCAL program (the
others have to be in programs in other languages included via the
external calls system). The resulting behaviour is entirely
inconsistent with the rest of the language, though, for what I hope
are obvious reasons.)
SO! 65535 LABELS AREN’T ENOUGH FOR YOU?
Legal values for line labels are 1 to 65535 (certain subranges are reserved for system and expansion libraries). This error comes up if you use nonpositive or twospot values for a line label.
NOTHING VENTURED, NOTHING GAINED
You used a variable that isn’t actually in your program. Failing that (which, contrary to previous versions of this manual, is indeed possible in the present version of C-INTERCAL, although I’m not telling how; a hint: what mechanism in C-INTERCAL allows for a computed variable number?), you specified an illegal number for a variable (legal numbers are positive and onespot). This error happens at compile time, at least for illegal variable numbers.
BUMMER, DUDE!
In INTERCAL, you’re allowed to
STASH as much as you like; this makes the language
Turing-complete and allows for unlimited recursion when combined
with computed COME FROM in the right way.
Unfortunately, real computers aren’t so idealised; if you
manage to write a program so memory-intensive that the computer
runs out of memory to store stashes, it causes this error at
runtime. To fix this error, you either have to simplify the program
or upgrade your computer’s memory, and even then that will
only help to some extent.
ERROR HANDLER PRINTED SNIDE REMARK
Arrays have to be large enough to hold at least one element; you tried to dimension an array which isn’t large enough to hold any data. This error happens at run time.
VARIABLES MAY NOT BE STORED IN WEST HYPERSPACE
This error happens at run time when the subscripts given to an
array are inconsistent with the way the array was dimensioned,
either because there were the wrong number of subscripts or because
a subscript was too large to fit in the array. It can also happen
when a multidimensional array is given to a command, such as
WRITE IN, that expects it to be monodimensional.
I’VE FORGOTTEN WHAT I WAS ABOUT TO SAY
This run-time error message is caused by the compiler running out of memory whilst trying to do I/O; at present, it can only happen during CLC-INTERCAL-style I/O.
THAT’S TOO HARD FOR MY TINY BRAIN
Some commands simply aren’t available in PIC-INTERCAL. I mean, PICs generally have less than a kilobyte of memory; you’re not going to be able to use some of the more confusing language features with that sort of resource limitation. The solution is to replace the affected command, or to not give the -P option (see -P) if you didn’t mean to compile as PIC-INTERCAL in the first place.
DON’T BYTE OFF MORE THAN YOU CAN CHEW
This error happens when there is an attempt to store a twospot value in a onespot variable. The actual size of the value is what matters when counting its spots; so you can store the output of a mingle in a onespot variable if it happens to be less than or equal to 65535, for instance. (This is not necessarily the case in versions of INTERCAL other than C-INTERCAL, though, so you have to be careful with portability when doing this.)
YOU CAN ONLY DISTORT THE LAWS OF MATHEMATICS SO FAR
Reverse assignments are not always mathematically possible. Also, sometimes they require changing the value of a constant; this is only legal if you specifically specified that it was legal by using the -v option. In the case of an impossible reverse assignment (including a situation in which operand overloading causes a reverse assignment to happen), this error happens at runtime.
This error can also come up when a scalar variable is overloaded to an array (which doesn’t make sense, but could happen if someone exploited bugs in the CREATE statement (see CREATE)), and an attempt is made to read or assign to that variable. (Subscripting a scalar variable is a syntax error, so there is no use for doing such an overload anyway.)
THAT MUCH QUOTATION AMOUNTS TO PLAGIARISM
There is a limit of 3200 on the number of nested spark/ears groups
allowed. If you somehow manage to exceed that limit, that will
cause this error. Try breaking the expression up into smaller
expressions. (The limit is trivial to increase by changing
SENESTMAX in ick.h; if you ever actually
come across a program that hits the limit but wasn’t designed
to, just email the maintainer to request a higher limit.)
YOU CAN’T HAVE EVERYTHING, WHERE WOULD YOU PUT IT?
Your program references so many variables that the compiler couldn’t cope. This error is unlikely to ever happen; if it does, try reducing the number of variables you use by combining some into arrays. This is a compile-time error.
THAT’S TOO COMPLEX FOR ME TO GRASP
This is another compile-time error that’s unlikely to ever happen; this one signifies the compiler itself running out of memory trying to compile your program. The only solutions to this are to simplify your program, or to make more memory available to the compiler.
I’M ALL OUT OF CHOICES!
Your program asked that a choicepoint be backtracked to or removed, but there aren’t any choicepoints at the moment. This runtime error usually indicates a logic mistake in your program. In backtracking programs translated from other backtracking languages, this indicates that the program has failed.
PROGRAM REJECTED FOR MENTAL HEALTH REASONS
Your program used a construct that only makes sense when
multithreading or backtracking (WHILE,
MAYBE, GO BACK, or GO
AHEAD), but you didn’t specify the -m
option (see -m). If you meant to write a
multithreaded or backtracking program, just give that option; if
you didn’t, be careful what words you use in comments! This
error happens at compile-time.
THROW STICK BEFORE RETRIEVING!
In order to RETRIEVE a variable, it has to be
STASHed first; if it isn’t, then this error
happens at runtime.
IT CAME FROM BEYOND SPACE
A COME FROM aiming at a line label — as opposed
to a computed COME FROM, which is allowed to be
pointing at a nonexistent line — must point to a valid line
label. The same applies to NEXT FROM. This error
happens at compile time if a nonexistent line label is found in one
of these contexts.
YOU WANT MAYBE WE SHOULD IMPLEMENT 64-BIT VARIABLES?
This error is like E275 (see E275), but applies when an attempt is made at runtime to store a threespot value (or even a fourspot or morespot value) in a twospot variable, or a threespot or greater value is produced as an intermediate during a calculation (for instance by a mingle operation). No values above twospot are allowed at any point during an INTERCAL program; if you want to process higher numbers, you have to figure out a different way of storing them.
BETTER LATE THAN NEVER
Oops! The compiler just noticed that it had a buffer overflow. (Normally programs catch buffer overflows before they happen; C-INTERCAL catches them just afterwards instead.) This only happens on systems which don’t have a modern C standard library. Try using shorter or fewer filenames on the command line, to reduce the risk of such an overflow.
FLOW DIAGRAM IS EXCESSIVELY CONNECTED
Aiming two COME FROMs at the same line only makes
sense in a multithreaded program. In a non-multithread program,
doing that will cause this error at compile time (if neither
COME FROM is computed) or at run time (if the command
that has just finished running is simultaneously the target of two
or more COME FROMs). This either indicates an error in
your program or that you’ve forgotten to use the
-m option (see -m) if you are
actually trying to split the program into two threads.
I DO NOT COMPUTE
The program asked for input, but for some reason it wasn’t
available. (This is a runtime error, obviously.) The error may
happen because the input is being piped in from a command or file
which has reached end-of-file, or because the user typed
CTRL-D
(UNIX/Linux) or CTRL-Z (DOS/Windows) while the program was trying to
WRITE IN some data.
WHAT BASE AND/OR LANGUAGE INCLUDES string?
When reading spelt-out-digit input, the input didn’t seem to be a valid digit in English, Sanskrit, Basque, Tagalog, Classical Nahuatl, Georgian, Kwakiutl, Volapük, or Latin. This seems to have languages covered pretty well; what on earth were you using, or did you just make a spelling mistake?
ERROR TYPE 621 ENCOUNTERED
The compiler encountered error E621 (see E621).
This happens at runtime when the program requests that no entries
are removed from the NEXT stack (which is possible),
but that the last entry removed should be jumped to (which given
the circumstances isn’t, because no entries were removed).
THE NEXT STACK RUPTURES. ALL DIE. OH, THE EMBARRASSMENT!
When an attempt is made to RESUME past the end of the
NEXT stack, the program ends; however, this cause the
program to end in a manner other than via GIVE UP or
DON'T TRY AGAIN, so an error message must be printed,
and this is that error message.
PROGRAM FELL OFF THE EDGE
You can’t just let execution run off the end of the program.
At least, that is, if it doesn’t end with TRY
AGAIN. An attempt to do that causes this error at runtime.
Note that if your program references the system library, then it
counts as being appended to your program and so the program will
run into the first line of the system library rather than cause
this error. As it happens, the first line of the system library is
a syntax error, so doing this will cause E000 (see E000) with the error text ‘PLEASE KNOCK
BEFORE ENTERING’. There isn’t a next statement
to be executed with E633, so the next statement won’t be
given in the error message.
HOW DARE YOU INSULT ME!
The PIN command doesn’t make much sense for
anything bigger than a PIC; using it in a
non-PIC program causes this error at
compile-time. Try using the normal input and output mechanisms
instead. This error may also be a clue that you are trying to
compile a PIC-INTERCAL program without giving the
-P option (see -P).
COMPILER HAS INDIGESTION
There isn’t a limit on the length of an input program other than your computer’s memory; if your computer does run out of memory during compilation, it causes this error. This error can also be caused if too many input files are specified on the command line; if you suspect this is the problem, split the compilation into separate compilations if you can, or otherwise you may be able to concatenate together your input files into larger but fewer files. Yet another potential cause of this error is if a line in an input program is too long; sensible line-wrapping techniques are encouraged.
RANDOM COMPILER BUG
No compiler is perfect; sometimes errors just happen at random. In this case, the random error is E774. If you don’t like the idea that your program may be shot down by a random compiler bug, or you are doing something important, you can use the -b option (see -b) to prevent this bug happening. (You may wonder why this bug is in there at all if it’s so easily prevented. The answer is that such a bug was present in the original INTERCAL-72 compiler, which also had an option to turn the bug off. It’s also a reward for people who actually read the manual.)
A SOURCE IS A SOURCE, OF COURSE, OF COURSE
You specified a file to compile on the command line, but the compiler couldn’t find or couldn’t open it. This is almost certainly because you made a typo specifying the file.
UNEXPLAINED COMPILER BUG
This should never come up, either at compile time or at run time. It could come up at either when an internal check by the compiler or the runtime libraries realises that something has gone badly wrong; mistakes happen, and in such cases the mistake will have been detected. (If this happens at compile time you can use the -U option (see -U) to cause the compiler to send an abort signal – which normally causes a core dump – when the error happens, to help debug what’s causing it.) More often, this error comes up when the operating system has noticed something impossible, like an attempt to free allocated memory twice or to write to a null pointer, and tells the compiler an error has occured, in which case the same response of putting up this error happens. The point is that in all cases this error indicates a bug in the compiler (even if it happens at run time); in such cases, it would be very helpful if you figure out what caused it and send a bug report (see Reporting Bugs).
ARE ONE-CHARACTER COMMANDS TOO SHORT FOR YOU?
This is a debug-time error caused when you give too much input to the debugger when all it wanted was to know what you wanted to do next.
PROGRAM IS TOO BADLY BROKEN TO RUN
There’s a limit to how many breakpoints you can have in a program; you’ve broken the limit and therefore broken the debugger. This is a debug-time error.
I HAVE NO FILE AND I MUST SCREAM
The output file couldn’t be written, maybe because the disk is full or because there’s already a read-only file with the same name. This is a compile-time error.
HELLO? CAN ANYONE GIVE ME A HAND HERE?
This error occurs at compile-time if a file type was requested for which the required libraries are unavailable. (Support for Funge does not ship with the compiler; instead, you need to generate the library yourself from the cfunge sources. For more information, see Creating the Funge-98 Library.)
FLAG ETIQUETTE FAILURE BAD SCOUT NO BISCUIT
This error occurs at runtime if an INTERCAL program was passed an unknown option flag.
YOU HAVE TOO MUCH ROPE TO HANG YOURSELF
There is no limit on the number of threads or choicepoints that you can have in a multithreaded or backtracking program (in a program that isn’t multithreaded or backtracking, these are obviously limited to 1 and 0 respectively). However, your computer may not be able to cope; if it runs out of memory in the multithreader, it will cause this error at runtime.
I GAVE UP LONG AGO
TRY AGAIN has to be the last command in a program, if
it’s there at all; you can’t even follow it by
comments, not even if you know in advance that they won’t be
REINSTATEd. This error happens at compile time if a
command is found after a TRY AGAIN.
NOCTURNAL EMISSION, PLEASE LAUNDER SHEETS IMMEDIATELY
This error should never happen, and if it does indicates a compiler bug. It means the emitter function in the code degenerator has encountered an unknown opcode. Please send a copy of the program that triggered it to the INTERCAL maintainers.
DO YOU REALLY EXPECT ME TO HAVE IMPLEMENTED THAT?
Some parts of the code haven’t been written yet. There ought to be no way to cause those to actually run; however, if you do somehow find a way to cause them to run, they will cause this error at compile time.
ILLEGAL POSSESSION OF A CONTROLLED UNARY OPERATOR
Some operators (such as whirlpool (@) and sharkfin
(^)) only make sense in TriINTERCAL
programs, and some have a minimum base in which they make sense.
This error happens at compile-time if you try to use an operator
that conflicts with the base you’re in (such as using
TriINTERCAL operators in an
INTERCAL program in the default base 2).
EXCUSE ME, YOU MUST HAVE ME CONFUSED WITH SOME OTHER COMPILER
This error occurs just before compile-time if a file is encountered on the command line that C-INTERCAL doesn’t recognise. (If this error occurs due to a ‘.a’, ‘.b98’, ‘.c’, ‘.c99’, or ‘.c11’ file, then you forgot to enable the external calls system using -e (see -e).)
NO SKELETON IN MY CLOSET, WOE IS ME!
The skeleton file ick-wrap.c or pickwrap.c is needed to be able to compile INTERCAL to C. If the compiler can’t find it, it will give this error message. This indicates a problem with the way the compiler has been installed; try using the -u option (see -u) to find out where it’s looking (you may be able to place a copy of the skeleton file in one of those places).
This is a list of the warnings stored in the warning database. Warnings only come up when the -l option (see -l) is given; even then, some of the warnings are not currently implemented and therefore will never come up.
DON’T TYPE THAT SO HASTILY
The positional precedence rules for unary operators are somewhat complicated, and it’s easy to make a mistake. This warning is meant to detect such mistakes, but is not currently implemented.
THAT WAS MEANT TO BE A JOKE
If an INTERCAL expression has been translated from another language such as C, the optimiser is generally capable of translating it back into something similar to the original, at least in base 2. When after optimisation there are still INTERCAL operators left in an expression, then this warning is produced. (Therefore, it’s likely to come up quite a lot if optimisation isn’t used!) The system library produces some of these warnings (you can tell if a warning has come up in the system library because you’ll get a line number after the end of your program).
THAT RELIES ON THE NEW WORLD ORDER
This warning comes up whenever the compiler recognises that you’ve added some code that didn’t exist in INTERCAL-72. This allows you to check whether your code is valid INTERCAL-72 (although -t (see -t) is more useful for that); it also warns you that code might not be portable (because INTERCAL-72 is implemented by most INTERCAL compilers, but more recent language features may not be).
SYSLIB IS OPTIMIZED FOR OBUSCATION
There is an idiom used in the system library that does a right-shift by selecting alternate bits from a twospot number and then mingling them the other way round. A rightshift can much more easily be done with a single rightshift, so this is a silly way to do it, and this warning warns that this idiom was used. However, the present optimizer is incapable of recognising whether this problem exists or not, so the warning is not currently implemented.
YOU CAN’T EXPECT ME TO CHECK BACK THAT FAR
It’s an error to assign a twospot value (a value over 65535) to a onespot variable, or to use it as an argument to a mingle. If the optimizer can’t guarantee at compile time that there won’t be an overflow, it issues this warning. (Note that this doesn’t necessarily mean there’s a problem — for instance, the system library generates some of these warnings — only that the optimiser couldn’t work out for sure that there wasn’t a problem.)
WARNING HANDLER PRINTED SNIDE REMARK
Your code looks like it’s trying to assign 0 to an array, giving it no dimension; this is an error. This warning is produced at compile time if it looks like a line in your code will cause this error, but it isn’t necessarily an error because that line of code might never be executed.
FROM A CONTRADICTION, ANYTHING FOLLOWS
It’s sometimes impossible to reverse an assignment (a reverse assignment can happen if the -v option (see -v) is used and an expression is placed on the left of an assignment, or in operand overloading); if the compiler detects that a reversal failure is inevitable, it will cause this warning. Note that this doesn’t always cause an error, because the relevant code might never be executed.
THE DOCUMENTOR IS NOT ALWAYS RIGHT
There is no way to get this warning to come up; it isn’t even written anywhere in C-INTERCAL’s source code, is not implemented by anything, and there are no circumstances in which it is even meant to come up. It is therefore not at all obvious why it is documented.
KEEP LOOKING AT THE TOP BIT
C-INTERCAL uses a slightly different typing mechanism to some other INTERCAL compilers; types are calculated at compile time rather than run time. This only makes a difference in some cases involving unary operators. It’s impossible to detect at compile time for certain whether such a case has come up or not, but if the compiler or optimizer thinks that such a case might have come up, it will issue this warning.
WARNING TYPE 622 ENCOUNTERED
Your code looks like it’s trying to resume by 0; this is an error. This warning is produced at compile time if it looks like a line in your code will cause this error, but it isn’t necessarily an error because that line of code might never be executed.
The C-INTERCAL distribution contains a runtime debugger
called ‘yuk’. Unlike most other debuggers, it is stored as
object code rather than as an executable, and it is compiled into the
code rather than operating on it. To debug code, add -y
(see -y) to the command line of
ick when invoking it; that tells it to compile the
debugger into the code and then execute the resulting combination. (The
resulting hybrid debugger/input executable is deleted afterwards; this
is to prevent it being run by mistake, and to prevent spreading the
debugger’s licence onto the code it was compiled with.)
yuk can also be used as a profiler using the -p option (see -p); this produces a file yuk.out containing information on how much time was spent running each command in your program, and does not prompt for debugger commands.
Note that some command line arguments are incompatible with the debugger, such as -m and -f. In particular, this means that multithreaded programs and programs that use backtracking cannot be debugged using this method; the +printflow option (see +printflow) to a compiled program may or may not be useful for debugging multithreaded programs.
When the debugger starts, it will print a copyright message and a message on how to access online help; then you can enter commands to run/debug the program. The debugger will show a command prompt, ‘yuk007 ’, to let you know you can input a command.
Here are the commands available. Commands are single characters
followed by newlines, or followed by a line number (in decimal) and a
newline or a variable name (a ., ,,
: or ; followed by a number in decimal; note
that some commands only allow onespot and twospot variables as
arguments).
| Command | Description |
|---|---|
| aLINE | All non-abstained commands on line LINE become abstained from once. |
| bLINE | A breakpoint is set on line LINE. The breakpoint causes execution with ‘c’ to stop when it is reached. |
| c | The program is run until it ends (which also ends the debugger) or a breakpoint is reached. |
| dLINE | Any breakpoint that may be on line LINE is removed. |
| eLINE | An explanation of the main expression in each command on line LINE is printed to the screen. The explanation is in the same format as the format produced by -h (see -h) and shows what the optimiser optimised the expression to (or the original expression if the optimiser wasn’t used). |
| fLINE | Removes the effect of the ‘m’ command on line LINE. |
| gLINE |
Causes the current command to be the first command on
LINE (if not on that line already) or the next command
on LINE, as if that line was NEXTed to and
then that NEXT stack item was forgotten.
|
| h | Lists 10 lines either side of the current line; if there aren’t 10 lines to one or the other side of the current line, instead more lines will be shown on the other side to compensate, if available. |
| iVAR |
Causes variable VAR to become IGNOREd,
making it read-only.
|
| jVAR |
Causes variable VAR to become REMEMBERed,
making it no longer read-only.
|
| k |
Continues executing commands until the NEXT stack is
the same size or smaller than it was before. In other words, if the
current command is not a NEXT and doesn’t have a
NEXT FROM aiming at it, one command is executed; but
if a NEXT does happen, execution will continue until
that NEXT returns or is forgotten. A breakpoint or the
end of the program also end this.
|
| lLINE | Lists 10 lines of source code either side of line LINE, the same way as with ‘h’, but using a line stated in the command rather than the current line. |
| mLINE | Produces a message onscreen every time a command on line LINE is executed, but without interrupting the program. |
| n |
Show the NEXT stack on the screen.
|
| o |
Continue executing commands until the NEXT stack is
smaller than it was before. If you are using NEXTs
like procedures, then this effectively means that the procedure
will run until it returns. A breakpoint or the end of the program
also end this.
|
| p | Displays the value of all onespot and twospot variables. |
| q | Aborts the current program and exits the debugger. |
| rLINE | Reinstates once all abstained commands on line LINE. |
| s | Executes one command. |
| t | Continues execution until the end of the program or a breakpoint: each command that executes is displayed while this command is running. |
| uLINE | Continues execution of the program until just before a command on line LINE is run (or a breakpoint or the end of the program). |
| vVAR | Adds a ‘view’ on variable VAR (which must be onespot or twospot), causing its value to be displayed on the screen whenever a command is printed on screen (for instance, because the command has just been stepped past, or due to the ‘m’ or ‘t’ commands). |
| w | Displays the current line and current command onscreen. |
| xVAR | Removes any view and any action that may be associated with it on variable VAR (which must be onespot or twospot). |
| yVAR | Adds a view on variable VAR; also causes a break, as if a breakpoint was reached, whenever the value of that variable changes. |
| zVAR | Adds a view on variable VAR; also causes a break, as if a breakpoint was reached, whenever that variable’s value becomes 0. |
| VAR | A onespot or twospot variable written by itself prints out the value of that variable. |
| <VAR |
WRITEs IN a new value for variable VAR.
Note that input must be in the normal ‘ONE TWO
THREE’ format; input in any other format will cause
error E579 (see E579) and as that is a fatal
error, the debugger and program it’s debugging will end.
|
| * |
Displays the license conditions under which ick is
distributed.
|
| ? | Displays a summary of what each command does. (‘@’ does the same thing.) |
While the code is executing (for instance, during a ‘c’, ‘k’, ‘o’, ‘t’ or ‘u’ command), it’s possible to interrupt it with CTRL-C (on UNIX/Linux) or CTRL-BREAK (on Windows/DOS); this will cause the current command to finish running and the debugger prompt to come back up.
INTERCAL programs consist of a list of statements. Execution of a program starts with its first statement; generally speaking each statement runs after the previous statement, although many situations can change this.
Whitespace is generally insignificant in INTERCAL programs; it cannot be added in the middle of a keyword (unless the keyword contains whitespace itself) or inside a decimal number, but it can be added more or less anywhere else, and it can be removed from anywhere in the program as well.
An INTERCAL statement consists of an optional line
label, a statement identifier, an optional execution chance, the
statement itself (see Statements), and
optionally ONCE or AGAIN.
The history of INTERCAL is plagued with multiple syntaxes and character sets. The result has settled down with two versions of the syntax; the original Princeton syntax, and the Atari syntax (which is more suited to the operating systems of today).
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| some versions | version 0.18+ | all versions | no |
The original INTERCAL-72 compiler was the Princeton compiler, which introduced what has become known as the Princeton syntax for INTERCAL; this is the syntax used in the original manual, for instance, and can be considered to be the ‘original’ or ‘official’ INTERCAL syntax. It is notable for containing various characters not found in some character sets; for instance, it writes the operator for mingle as a cent sign (known as ‘change’). The other operator that often causes problems is the bookworm operator ‘V’, backspace, ‘-’, which is used for exclusive-or; the backspace can cause problems on some systems (which was probably the original intention). This syntax is also the default syntax in the CLC-INTERCAL compiler, which is the de facto standard for expanding the Princeton syntax to modern INTERCAL features that are not found in INTERCAL-72; however, it does not appear to have been used as the default syntax in any other compilers. Nowadays, there are other ways to write the required characters than using backspace; for instance, the cent sign appears in Latin-1 and UTF-8, and there are various characters that approximate bookworms (for instance, CLC-INTERCAL uses the Latin-1 yen symbol for this, which just to make things confusing, refers to a mingle in modern Atari syntax).
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| some versions | yes | version 0.05+ | yes |
The other main syntax is the Atari syntax, so called because it was originally described in notes about an “Atari implementation” added to the paper INTERCAL-72 manual when it was softcopied in 1982. These notes describe a never-completed compiler implementation for 6502 by Mike Albaugh and Karlina Ott; it was meant to use the Atari 800 cartrtidge and screen editor, but that portion was never written. The syntax was designed to work better on ASCII-based systems, by avoiding the change character (although it can still be written as ‘c’, backspace, ‘/’, which the Atari compiler documentation claims that the Princeton compiler supported) in favour of a ‘big money’ character (‘$’), and using the ‘what’ (‘?’) as an alternative character for exclusive-or. This is the syntax that C-INTERCAL and J-INTERCAL have always used, and is the one most commonly used for communicating INTERCAL programs on Usenet and other similar fora (where ASCII is one of the most reliable-to-send character sets). It is also the syntax used for examples in this manual, for much the same reason. The Atari syntax for constructs more modern than INTERCAL-72 is normally taken to be that used by the C-INTERCAL compiler, because it is the only Atari-syntax-based compiler that contains non-INTERCAL-72 constructs that actually need their own notation.
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| yes | all versions | all versions | all versions |
The first part of an INTERCAL statement is a line label that specifies what its line number is. This is optional; it’s legal to have a statement without a line number, although that prevents other commands referring to it by number. Line numbers must be constants, and unique within the program. However, they do not have to be in order; unlike some other languages with line numbers, a line with a higher number can come earlier in the program than a line with a lower number, and the numbers don’t affect the order in which commands are executed.
A line label is a integer expressed in decimal within a wax/wane pair
(( and )). For instance, this is a valid line
label:
(1000)
Note that line numbers from 1000 to 1999 are used by the system library, so using them within your own programs may produce unexpected errors if the system library is included. Apart from this, line numbers from 1 to 65535 are allowed.
It has become reasonably customary for people writing INTERCAL libraries to pick a range of 1000 line numbers (for instance, 3000 to 3999) and stick to that range for all line numbers used in the program (apart from when calling the system library), so if you want to write an INTERCAL library, it may be a good idea to look at the existing libraries (in the pit/lib directory in the C-INTERCAL distribution) and choose a range of numbers that nobody else has used. If you aren’t writing a library, it may be a good idea to avoid such number ranges (that is, use only line numbers below 1000 or very high numbers that are unlikely to be used by libraries in the future), so that you can easily add libraries to your program without renumbering in the future.
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| yes | all versions | all versions | all versions |
After the line label (if a statement has one) comes the statement identifier, which marks where the statement starts. Either the label or the statement identifier, whichever one comes first, marks where the preceding statement finishes.
The main statement identifier is DO. It also has two
synonyms, PLEASE and PLEASE DO; these
synonyms are the ’polite’ forms of statement identifiers.
Although the three identifiers have the same meaning, using either
polite or non-polite identifiers too much can cause an error; the
correct proportion is approximately 3 non-polite identifiers for every
polite identifier used. None of these identifiers actually does
anything else apart from marking where the statement starts; they leave
the statements in the default ‘reinstated’ state.
Adding NOT or N'T to the end of any of these
identifiers, to create a statement identifier such as DO
NOT or PLEASE DON'T, also creates a valid statement
identifier. These differ in meanings from the previous set of
identifiers, though; they cause the statement they precede to not be
executed by default; that is, the command will be skipped during
execution (this is known as the ‘abstained’ state). This
applies even if the command in question is in fact a syntax error, thus
causing this to be a useful method of writing comments. One common
idiom is to write code like this:
PLEASE NOTE: This is a comment.
The statement identifier (PLEASE NOT) is the only part of
this statement that is valid INTERCAL; however,
because the statement identifier is in the negated form that contains
NOT, the syntax error won’t be executed, and
therefore this is a valid statement. (In INTERCAL,
syntax errors happen at runtime, so a program containing a statement
like DOUBT THIS WILL WORK will still compile, and will not
end due to the syntax error unless that statement is actually executed.
See E000.)
The ABSTAIN and REINSTATE statements can
override the NOT or otherwise on a statement identifier;
see ABSTAIN.
In backtracking programs, MAYBE is also a valid statement
identifier; see MAYBE. It comes before the other
keywords in the statement identifier, and an implicit DO
is added if there wasn’t one already in the statement identifier
(so MAYBE, MAYBE DO, MAYBE
DON'T, MAYBE PLEASE, and so on are all valid
statement identifiers).
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| yes | all versions | version 0.02+ | all versions |
It’s possible to specify that a command should be run only a
certain proportion of the time, at random. This is a rarely used
feature of INTERCAL, although it is the only way to
introduce randomness into a program. (The C-INTERCAL
compiler approximates this with pseudorandomness.) An execution chance
specification comes immediately after the statement identifier, but
before the rest of the statement, and consists of a double-oh-seven
(%) followed by an integer from 1 to 99 inclusive, written
in decimal; this gives the percentage chance of the statement running.
The execution chance only acts to prevent a statement running when it
otherwise would have run; it cannot cause a statement that would
otherwise not have run to run. For instance, the statement DO %40
WRITE OUT #1 has a 40% chance of writing out
‘I’, but the statement DON'T %40 WRITE
OUT #1 has no chance of writing out I or anything
else, because the N'T prevents it running and the
double-oh-seven cannot override that.
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| no | version 0.25+ | no | no |
The last part of a statement is an optional ONCE or
AGAIN. ONCE specifies that the statement is
self-abstaining or self-reinstating (this will be explained below);
AGAIN specifies that the statement should behave like it
has already self-reinstated or self-abstained. Whether the behaviour is
self-abstention or self-reinstatement depends on whether the statement
was initially abstained or not; a ONCE on an initially
reinstated statement or AGAIN on an initially abstained
statement indicates a self-abstention, and a ONCE on an
initially abstained statement or AGAIN on an initially
reinstated statement indicates a self-reinstatement.
The first time a self-abstaining statement is encountered, it is
executed as normal, but the statement is then abstained from and
therefore will not run in future. Likewise, the first time a
self-reinstating statement is encountered, it is not executed (as is
normal for an abstained statement), but then becomes reinstated and
will run in future. In each of these cases, the ONCE
effectively changes to an AGAIN; the ONCE
only happens once, as might be expected.
REINSTATING a currently abstained self-abstaining
statement or ABSTAINING (that is, with the
ABSTAIN or REINSTATE commands) a currently
reinstated self-reinstating statement causes the AGAIN on
the statement to change back into a ONCE, so the statement
will again self-abstain or self-reinstate. Likewise,
REINSTATING a currently abstained self-reinstating
statement or ABSTAINING a currently reinstated
self-abstaining statement causes its ONCE to turn into an
AGAIN.
Historical note: ONCE was devised by Malcom Ryan as a
method of allowing synchronisation between threads in a multithreaded
program (ONCE is atomic with the statement it modifies,
that is, there is no chance that threads will change between the
statement and the ONCE). AGAIN was added to
Malcom Ryan’s Threaded Intercal standard on the suggestion of
Kyle Dean, as a method of adding extra flexibility (and to allow the
ONCEs to happen multiple times, which is needed to
implement some multithreaded algorithms).
Many INTERCAL statements take expressions as arguments. Expressions are made up out of operands and operators between them. Note that there is no operator precedence in INTERCAL; different compilers resolve ambiguities different ways, and some versions of some compilers (including the original INTERCAL-72 compiler) will cause error messages on compiling or executing an ambiguous expression, so it’s safest to fully group each expression.
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| yes | all versions | all versions | all versions |
The basic operands in INTERCAL are constants and variables. These together make up what in other languages are known as ‘lvalues’, that is, operands to which values can be assigned. (Constants can also be lvalues in INTERCAL, but by default C-INTERCAL turns this off because it carries an efficiency penalty and can be confusing; this can be turned on with the -v option (see -v).)
Constants can have any integer value from 0 to 65535 inclusive; higher
values (up to 4294967295) can be generated in programs, but cannot be
specified literally as constants. (The usual way to work around this
limitation is to interleave two constants together; see Mingle.) A constant is written as a mesh (#)
followed by a number in decimal. At the start of the program, all
constants have the same value as the number that identifies them; for
instance, #100 has 100 as its value, and it’s
strongly advised not to change the value of a constant during the
execution of a program.
There are four types of variable: 16-bit and 32-bit unsigned integers,
and arrays of 16-bit and 32-bit unsigned integers. These are
represented with a spot, twospot, tail, and hybrid (.,
:, ,, and ;) respectively. For
this reason, integers within the range 0 to 65535 inclusive are known
as ‘onespot numbers’, and integers within the range 0 to
4294967295 inclusive are known as ‘twospot numbers’;
variables with those ranges are known as onespot and twospot variables.
(Note that arrays did not work in C-INTERCAL before
version 0.7.)
Variables are represented with a character representing their data
type, followed by an integer from 1 to 65535 inclusive, written in
decimal. Non-array variables don’t need to be declared before
they are used; they automatically exist in any program that uses them.
For instance, .1 and .001 are the same
variable, onespot number 1. Array variables need to be dimensioned
before they are used, by assigning dimensions to them; see Calculate.
Because there are no operator precedences in INTERCAL, there are various solutions to specifying what precedences actually are.
All known versions of INTERCAL accept the
INTERCAL-72 grouping rules. These state that
it’s possible to specify that an operator takes precedence by
grouping it inside sparks (') or rabbit-ears
("), the same way as wax/wane pairs (parentheses) are
used in other programming languages. INTERCAL-72 and
earlier C-INTERCAL versions demanded that expressions
were grouped fully like this, and this practice is still
recommended because it leads to portable programs and is easier to
understand. Whether sparks or rabbit-ears (often called just
‘ears’ for short) are used normally doesn’t
matter, and programmers can use one or the other for clarity or for
aesthetic appeal. (One common technique is to use just sparks at
the outermost level of grouping, just ears at the next level, just
sparks at the next level, and so on; but expressions like
''#1~#2'~"#3~#4"'~#5 are completely unambiguous, at
least to the compiler.)
There are, however, some complicated situations involving array subscripting where it is necessary to use sparks and ears at alternate levels, if you want to write a portable program. This limitation is in C-INTERCAL to simplify the parsing process; INTERCAL-72 has the same limitation, probably for the same reason. Compare these two statements:
DO .1 <- ,3SUB",2SUB.1".2 DO .1 <- ,3SUB",2SUB.1".2~.3"".4
The problem is that in the first statement, the ears close a group, and in the second statement, the ears open a group, and it’s impossible to tell the difference without unlimited lookahead in the expression. Therefore, in similar situations (to be precise, in situations where a group is opened inside an array subscript), it’s necessary to use the other grouping character to the one that opened the current group if you want a portable program.
One final comment about sparks and rabbit-ears; if the next
character in the program is a spot, as often happens because
onespot variables are common choices for operands, a spark and the
following spot can be combined into a wow (!).
Unfortunately, the rabbit-ear/spot combination has no one-character
equivalent in any of the character sets that
C-INTERCAL accepts as input (UTF-8, Latin-1, and
ASCII-7) as none of these contain the rabbit character, although
the Hollerith input format that CLC-INTERCAL can use
does.
The precedence rules used by CLC-INTERCAL for grouping
when full grouping isn’t used are simple to explain: the
largest part of the input that looks like an expression is taken to
be that expression. The main practical upshot of this is that
binary operators right-associate; that is, .1~.2~.3 is
equivalent to .1~'.2~.3'. C-INTERCAL
versions 0.26 and later also right-associate binary operators so as
to produce the same results as CLC-INTERCAL rules in
this situation, but as nobody has yet tried to work out what the
other implications of CLC-INTERCAL rules are they are
not emulated in C-INTERCAL, except possibly by chance.
In INTERCAL-72 and versions of C-INTERCAL
before 0.26, unary operators were always in the ‘infix’
position. (If you’re confused about how you can have an infix
unary operator: they go one character inside a group that they
apply to, or one character after the start of a constant or
variable representation; so for instance, to portably apply the
unary operator & to the variable :1,
write :&1, and to portably apply it to the
expression '.1~.2', write '&.1~.2'.)
CLC-INTERCAL, and versions of C-INTERCAL
from 0.26 onwards, allow the ‘prefix’ position of a
unary operator, which is just before whatever it applies to (as in
&:1). This leads to ambiguities as to whether an
operator is prefix or infix. The portable solution is, of course,
to use only infix operators and fully group everything, but when
writing for recent versions of C-INTERCAL, it’s
possible to rely on its grouping rule, which is: unary operators
are interpreted as infix where possible, but at most one infix
operator is allowed to apply to each variable, constant, or group,
and infix operators can’t apply to anything else. So for
instance, the C-INTERCAL
'&&&.1~.2' is equivalent to the portable
'&"&.&1"~.2' (or the more readable version
of this, "&'"&.&1"~.2'", which is also
portable). If these rules are counter-intuitive to you, remember
that this is INTERCAL we’re talking about;
note also that this rule is unique to C-INTERCAL, at
least at the time of writing, and in particular
CLC-INTERCAL is likely to interpret this expression
differently.
Operators are used to operate on operands, to produce more complicated expressions that actually calculate something rather than just fetch information from memory. There are two types of operators, unary and binary operators, which operate on one and two arguments respectively. Binary operators are always written between their two operands; to portably write a unary operator, it should be in the ‘infix’ position, one character after the start of its operand; see Prefix and infix unary operators for the full details of how to write unary operators portably, and how else you can use them if you aren’t aiming for portability. This section only describes INTERCAL-72 operators; many INTERCAL extensions add their own operators.
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| yes | all versions | all versions | all versions |
Mingle, or interleave, is one of the two binary operators in INTERCAL-72. However, different INTERCAL compilers represent it in different ways, so it is impossible to write a mingle in a program completely portably, because it differs between Princeton and Atari syntax, and worse, the sequence of character codes needed to represent it in each syntax has varied from compiler to compiler.
The original INTERCAL-72 compiler (the Princeton compiler)
used the ’change’ (cent) character for a mingle,
represented as c, backspace, /. (By the way,
this is still the most portable way to write a mingle; both
C-INTERCAL and CLC-INTERCAL accept it, at
least if a lowercase c is used, the Atari compiler was to
accept it, and its documentation claimed that the Princeton compiler
also accepted it; CLC-INTERCAL also accepts a capital
C before the backspace and /, and allows
| rather than /.) The uncompleted Atari
compiler intended to use a ’big money’ character
($) as the mingle character; this character is also the
only one accepted for mingle by the J-INTERCAL compiler.
C-INTERCAL originally also used the $
character for mingle, and this character is the one most commonly seen
in existing C-INTERCAL programs, and most often used when
giving examples of INTERCAL on Usenet, because it
exists in the ASCII-7 character set, and because it doesn’t
contain control characters. From version 0.18 of
C-INTERCAL onwards, various other units of currency
(change, quid, and zlotnik if Latin-1 is used as the input, and euro if
Latin-9 is used as the input) are accepted; from version 0.20 onwards,
in addition to the Latin-1 characters, all the currency symbols in
Unicode are accepted if UTF-8 is used as the input format.
CLC-INTERCAL has always used the change character (either
the Latin-1 version or the version that contains a backspace) for
mingle. In this manual, mingle will be represented as $,
but it’s important to bear in mind that this character is not the
most portable choice.
The mingle operator should be applied to two operands or expressions. To be portable, the operands must both be onespot expressions, that is expressions which have a 16-bit result; C-INTERCAL relaxes this rule slightly and only requires that the result be in the onespot range. (This is because the data type of a select operator’s value is meant to be determined at runtime; C-INTERCAL determines all data types at compile time, so has to guess a 32-bit result for a select with a 32-bit type as its right operand even when the result might actually turn out to be of a 16-bit type, and so this behaviour prevents an error when a select operation returns a value with a 16-bit data type and is used as an argument to a mingle.) The result is a 32-bit value (that is, it is of a 32-bit data type, even if its value fits into the onespot range), which consists of bits alternated from the two arguments; to be precise, its most significant bit is the most significant bit of its first argument, its second most significant bit is the most significant bit of its second argument, its third most significant bit is the second most significant bit of its first argument, and so on until its least significant bit, which is the least significant bit of its second argument.
One of the most common uses of interleaving is to create a constant
with a value greater than 65535; for instance, 65536 is
#0$#256. It is also commonly used in expressions that need
to produce 32-bit results; except in some simple cases, this is usually
coded by calculating separately the odd-numbered and even-numbered bits
of the result, and mingling them together at the end. It is also used
in expressions that need to left-shift values or perform similar
value-increasing operations, as none of the other operators can easily
do this; and mingle results are commonly used as the argument to unary
binary logic operators, because this causes them to behave more like
the binary logic operators found in some other languages.
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| yes | all versions | all versions | all versions |
The select operator is one of the two binary operators in
INTERCAL-72; unlike mingle, every known implementation of
INTERCAL ever has used the sqiggle character
(~) as the representation of the select operator, meaning
that writing it portably is easy.
The select operator takes two arguments, which can be of either
datatype (that is, 16- or 32-bit). It returns a value made by selecting
certain bits of its first operand indicated by the second operand, and
right-justifying them. What it does is that it ignores all the bits of
the first operand where the second operand has a 0 as the corresponding
bit, that is, deletes them from a copy of the operand’s value;
the bits that are left are squashed together towards the
least-significant end of the number, and the result is filled with 0s
to make it up to 16 or 32 bits. (In INTERCAL-72 the
minimum multiple of 16 bits possible that the result fits into is
chosen, although if :1 has the value 131061 (in hex, 1FFFF) the
expression #21~:1 produces a 32-bit result because 17 bits
were selected, even though many of the leading bits were zeros; in
C-INTERCAL the data type of the result is the same as of
the right operand of the select, so that it can be determined at
compile time, and so using a unary binary logic operator on the result
of select when the right operand has a 32-bit type is nonportable and
not recommended.) As an example, #21~:1 produces 21 as its
result if :1 has the value 131061, 10 as its result if :1 has the value
30 (1E in hex; the least significant bit of 21 is removed because it
corresponds to a 0 in :1), and 7 as its result if :1 has the value 21
(because three bits in 21 are set, and those three bits from 21 are
therefore selected by 21).
Select is used for right-shifts, to select every second bit from a number (either to produce what will eventually become an argument to mingle, or to interpret the result of a unary binary logic operator, or occasionally both), to test if a number is zero or not (by selecting it from itself and selecting 1 from the result), in some cases as a limited version of bitwise-and (that only works if the right operand is 1 less than a power of 2), and for many other purposes.
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| yes | all versions | all versions | all versions |
There are three unary operators in INTERCAL-72, each of
which carries out a binary logic operation on adjacent bits of the
number. The operators are and, or, and exclusive or; and and or are
represented by an ampersand (&) and book
(V) respectively, and exclusive or has the same notational
problems as mingle, as it differs between Princeton and Atari syntax.
It was represented by a bookworm, written V, backspace,
-, in the Princeton INTERCAL-72
implementation, and this is still the most portable way to write it
(C-INTERCAL and CLC-INTERCAL accept it). The
Atari implementation of INTERCAL-72 wrote it with a what
(?), and this is the representation originally used by
C-INTERCAL (and still accepted), the only representation
accepted by J-INTERCAL, the one most commonly used on
Usenet, and the one used in this manual (although again, it’s
worth pointing out that this isn’t portable).
CLC-INTERCAL approximates a bookworm with the yen
character, which being a currency character is one of the possible
representations for mingle in C-INTERCAL;
C-INTERCAL uses the rather confusing method of
interpreting a yen character as exclusive-or if input in Latin-1 but as
mingle if input in UTF-8. (This usually does the right thing, because
CLC-INTERCAL doesn’t support UTF-8.) In the same
way, CLC-INTERCAL has a C-INTERCAL
compatibility option to allow the use of ? for
exclusive-or.
The operators take each pair of consecutive bits in their arguments
(that is, the least significant with the second least significant, the
second least significant with the third least significant, the third
least significant with the fourth least significant, and so on, with
the pair consisting of the most significant and least significant being
used to calculate the most significant bit of the result), and perform
an appropriate logic operation on them; and sets a bit of the result if
and only if both bits in the pair were set, or sets each bit
corresponding to each pair where either bit was set, and exclusive or
sets if and only if the bits in the pair had different values (that is,
one was set, but not both). So for instance, #&26 is
16 (26 is 1A in hexadecimal or 11010 in binary); #V26 is
31 (11111 in binary), and #?26 is 23 (10111 in binary).
The most commonly seen use for these operators is to carry out bitwise ands, ors, and exclusive ors between two different 16-bit expressions, by mingling them together, applying a unary binary logic operator, and selecting every second bit of the result; such code often results due to people thinking in terms of some other language when writing INTERCAL, but is still often useful. (Historically, the first idiom added to the optimizer, apart from constant folding, was the mingle/unary/select sequence.) There are more imaginative uses; one impressive example is the exclusive or in the test for greater-than from the original INTERCAL-72 system library:
DO :5 <- "'?":1~'#65535$#0'"$":2~'#65535$#0'"'
~'#0$#65535'"$"'?":1~'#0$#65535'"$":2~'#0$
#65535'"'~'#0$#65535'"
DO .5 <- '?"'&"':2~:5'~'"'?"'?":5~:5"~"#65535~
#65535"'~'#65535$#0'"$#32768'~'#0$#65535'"
$"'?":5~:5"~"#65535$#65535"'~'#0$#65535'"'
"$"':5~:5'~#1"'~#1"$#2'~#3
The first statement works out the value of :1 bitwise exclusive or :2; the second statement then works out whether the most significant set bit in :5 (that is, the most significant bit that differs between :1 and :2) corresponds to a set bit in :2 or not. In case that’s a bit too confusing to read, here’s the corresponding optimizer idiom (in OIL):
((_1~:2)~((?32(:2~:2))^#2147483648))->(_1>(:2^_1))
(Here, the ^ refers to a bitwise exclusive or, an operation found in OIL but not in INTERCAL, which is why the INTERCAL version is so much longer.) The INTERCAL version also has some extra code to check for equality and to produce 1 or 2 as the output rather than 0 or 1.
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| yes | version 0.7+ | all versions | all versions |
In order to access the elements of an array, either to read or write
the array, it is necessary to use the array subscript operator
SUB. Note that an array element is not a variable, so it
is not accepted as an acceptable argument to statements like
IGNORE; however, it can be assigned to.
The syntax for an array element is the array, followed by the keyword
SUB, followed by an expression for the element number in
the array. In the case of a multidimensional array, more than one
expression is given after the keyword SUB to give the
location of the element in each of the array’s dimensions. The
first element in an array or array dimension is numbered 1.
For instance, this is a legal (but not particularly useful) INTERCAL program with no syntax errors that shows some of the syntaxes possible with array subscripting:
PLEASE ,1 <- #2 DO .1 <- #2 DO ,1 SUB .1 <- #1 DO ,1 SUB #1 <- ,1 SUB #2 PLEASE ;1 <- #2 BY #2 DO ;1 SUB #1 #2 <- ,1 SUB ,1 SUB .1 DO READ OUT ;1SUB#1.1 DO GIVE UP
Grouping can get complicated when nested array subscripting is used, particularly with multiple subscripts. It is the programmer’s job to write an unambiguous statement, and also obey the extra grouping rules that apply to array subscripts; see Grouping Rules.
There is a wide range of statements available to INTERCAL programs; some identifiably belong to a particular variant or dialect (such as Backtracking INTERCAL), but others can be considered to be part of the ’core language’. The statements listed here are those that the C-INTERCAL compiler will accept with no compiler switches to turn on particular dialect options. Note that many statements have slightly different effects in different implementations of INTERCAL; known incompatibilities are listed here, but it’s important to check your program on multiple compilers when attempting to write a portable program.
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| yes | version 0.15+ | all versions | all versions |
One of the more commonly-used commands in INTERCAL is the syntax error. A properly-written syntax error looks nothing like any known INTERCAL command; a syntax error that looks vaguely like a command but isn’t may confuse C-INTERCAL before version 0.28, and possibly other compilers, into bailing out at compile time in some situations (this is known as a ‘serious syntax error’), and so is not portable. For other syntax errors, though, the semantics are easily explained: there is a run-time error whenever the syntax error is actually executed, and the line containing the syntax error is used as the error message.
One purpose of this is to allow your programs to produce their own custom errors at run time; however, it’s very important to make sure that they start and end in the right place, by manipulating where statement identifiers appear. Here’s a correct example from the system library:
DOUBLE OR SINGLE PRECISION ARITHMETIC OVERFLOW
This is a valid INTERCAL command, that produces an
error when run (note the DO at the start). An even more
common use is to produce an initially abstained syntax error by using
an appropriate statement identifier, for instance
PLEASE NOTE THAT THIS IS A COMMENT
This would produce an error if reinstated somehow, but assuming that
this isn’t done, this is a line of code that does nothing, which
is therefore equivalent to a comment in other programming languages.
(The initial abstention is achieved with the statement identifier
PLEASE NOT; the extra E causes the command to
be a syntax error, and this particular construction is idiomatic.)
Referring to the set of all syntax errors in a program (or the set of
all commands of any other given type) is achieved with a special
keyword known as a ‘gerund’; gerund support for syntax
errors is resonably recent, and only exists in
CLC-INTERCAL (version 1.-94.-3 and later, with
COMMENT, COMMENTS, or
COMMENTING), and C-INTERCAL
(COMMENT in version 0.26 and later, and also
COMMENTS and COMMENTING in version 0.27 and
later). Therefore, it is not portable to refer to the set of all syntax
errors by gerund; using a line label is a more portable way to refer to
an individual syntax-error command.
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| yes | all versions | all versions | all versions |
At present, the only INTERCAL command that contains
no keywords (apart from the statement identifier and possibly
ONCE or AGAIN) is what is known as the
‘calculate’ command. It is used to assign values to
variables, array elements, and arrays; assigning a value to an array
changes the number of elements that that array can hold, and causes the
values of all elements previously in that array to be lost. The syntax
of a calculate command is as follows:
DO .1 <- ':2~:3'~#55
That is, the command is written as a variable or array element, then
the <- operator (known as an ‘angle-worm’
and pronounced ‘gets’), then an expression to assign to it.
In the special case when an array is being dimensioned by assigning a
value to it, the expression can contain the keyword BY to
cause the array to become multidimensional; so for a 3 by 4 by 5 array,
it would be possible to write
DO ,1 <- #3 BY #4 BY #5
The calculate command always evaluates the expression, even if for some reason the assignment can’t be done (for instance, if the variable being assigned to is read-only); this is important if the expression has side-effects (for instance, giving an overflow error). If the variable does happen to be read-only, there is not an error; the expression being assigned to it is just evaluated, with the resulting value being discarded.
The gerund to refer to calculations is CALCULATING;
however, if you are planning to use this, note that a bug in older
versions of C-INTERCAL means that assignments to arrays
are not affected by this gerund before version 0.27.
CLC-INTERCAL from 1.-94.-4 onwards, and
C-INTERCAL from 0.26 onwards, allow arbitrary expressions
on the left hand side of an assignment (C-INTERCAL only if
the -v option is used); for more information on how such
‘reverse assignments’ work, see Operand Overloading.
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| yes | all versions | see text | all versions |
The only flow-control commands in INTERCAL-72 were
NEXT, RESUME, and FORGET;
together these manipulate a stack of locations in the program known as
the ‘NEXT stack’. Although all INTERCAL
compilers have implemented these, from CLC-INTERCAL
version 0.05 onwards CLC-INTERCAL has considered them
obsolete, and therefore a special command-line switch needs to be used
to enable them. (They are still the most portable flow-control commands
currently available, though, precisely because INTERCAL-72
implements nothing else.) Note that there is a strict limit of 80
locations on the NEXT stack, enforced by all known
INTERCAL compilers; this helps to enforce good
programming style, by discouraging NEXT-stack leaks (which are
otherwise quite easy to write).
Here are examples to show the syntax of these three statements:
DO (1000) NEXT DO FORGET '.1~.1'~#1 DO RESUME .5
The NEXT command takes a line label as its argument
(unlike most other INTERCAL commands, it comes after
its argument rather than before); both FORGET and
RESUME take expressions. (CLC-INTERCAL from
version 0.05 onwards also allows an expression in NEXT,
rather than a label, to give a computed NEXT, but this
behaviour was not implemented in other compilers, and is deprecated in
CLC-INTERCAL along with noncomputed NEXT; if
computed NEXT is ever implemented in
C-INTERCAL, it will likely likewise be deprecated upon
introduction). (Update: it was implemented in C-INTERCAL
version 0.28, but only as part of the external calls system, so it
cannot be used in ordinary programs; a sample expansion library gives
in-program access to a limited form of computed NEXT, but
should probably not be used.) Running a NEXT causes the
program control to transfer to the command whose line label is
referenced, and also saves the location in the program immediately
after the NEXT command on the top of the NEXT stack.
In order to remove items from the NEXT stack, to prevent
it filling up (which is what happens with a naive attempt to use the
NEXT command as an equivalent to what some other languages
call GOTO), it is possible to use the FORGET or
RESUME commands. They each remove a number of items from
the NEXT stack equal to their argument; RESUME also
transfers control flow to the last location removed from the
NEXT stack this way. Trying to remove no items, or more
items than there are in the stack, does not cause an error when
FORGET is used (no items or all the items are removed
respectively); however, both of these cases are errors in a
RESUME statement.
Traditionally, boolean values in INTERCAL programs
have been stored using #1 and #2 as the two logic levels. This is
because the easiest way to implement an if-like construct in
INTERCAL-72 is by NEXTING, then
NEXTING again, then RESUMING either by 1 or 2
according to an expression, and then if the expression evaluated to 1
FORGETTING the remaining NEXT stack entry. By the way, the
previous sentence also explained what the appropriate gerunds are for
NEXT, RESUME, and FORGET.
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| yes | all versions | all versions | all versions |
The NEXT stack is not the only stack available in an
INTERCAL program; each variable used in the program
also has its own stack, which holds values of the same type as the
variable. The STASH command pushes a variable’s
value onto that variable’s stack; RETRIEVE can be
used in the same way to pop the top element of a variable’s stack
to replace that variable’s value. The syntax is the same as most
other INTERCAL commands, with the word
STASH or RETRIEVE followed by the variable or
variables to stash or retrieve:
DO STASH .1 + ;2 DO RETRIEVE ,3
Note that it is possible to stash or retrieve multiple variables at
once, by listing their names separated by intersections
(+); it’s even possible to stash or retrieve a
variable twice in the same statement.
It is not entirely clear how RETRIEVE interacts with
IGNORE in historical INTERCAL-72 compilers;
the three modern INTERCAL compilers all use
different rules for the interaction (and the C-INTERCAL
maintainers recommend that if anyone decides to write their own
compiler, they choose yet another different rule so that looking at the
interaction (the so-called ‘ignorret test’) can be used as
a method of determining which compiler is running):
RETRIEVE simply allows a change to its value despite the
read-only status.
The appropriate gerunds for STASH and
RETRIEVE are STASHING and
RETRIEVING respectively.
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| yes | all versions | all versions | all versions |
Variables in INTERCAL can be either read-write or
read-only. At the start of a program, all variables are read-write, but
this status can be changed dynamically during execution of a program
using the IGNORE and REMEMBER statements
(whose gerunds are IGNORING and REMEMBERING
respectively). The syntax is the same as for STASH and
RETRIEVE: the command’s name followed by an
intersection-separated list of variables. For instance:
DO IGNORE .4 DO REMEMBER ,4 + ;5
Using the IGNORE statement sets a variable to be read-only
(or does nothing if it’s read-only already);
REMEMBER sets it to be read-write. Any attempt to assign
to a read-only variable silently fails. One place that this is used is
in the system library; instead of not assigning to a variable in
certain control flow paths, it instead sets it to be read-only so that
subsequent assignments don’t change its value (and sets it to be
read-write at the end, which succeeds even if it was never set
read-only in the first place); the advantage of this is that it
doesn’t need to remember what flow path it’s on except in
the variable’s ignorance status.
The interaction between IGNORE and RETRIEVE
was never defined very clearly, and is in fact different in
C-INTERCAL, CLC-INTERCAL and
J-INTERCAL; for more details, see RETRIEVE.
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| yes | all versions | all versions | all versions |
The statement identifier of a statement determines whether it’s
in an abstained or reinstated state at the start of a program; these
states determine whether the statement runs at all when it’s
encountered. It is, however, possible to change this state dynamically
during a program’s execution, and the statements to do this are
rather appropriately named ABSTAIN and
REINSTATE. There are two forms of each, one which takes a
single line label (which must be constant in most compilers, but can
instead be an expression in recent CLC-INTERCAL versions),
and one which takes an intersection-delimited list of gerunds. They
look like this:
DO ABSTAIN FROM ABSTAINING + REINSTATING DO ABSTAIN FROM (10) DO REINSTATE CALCULATING DO REINSTATE (22)
(This also illustrates the gerunds used for these commands; note that
ABSTAINING from REINSTATING is generally a
bad idea!) The line referenced, or every command represented by any
gerund referenced, are reinstated or abstained as appropriate
(effectively changing the DO to DON’T (or PLEASE to PLEASE
DON’T, etc.), or vice versa). Using these forms of
ABSTAIN and/or REINSTATE won’t abstain
from a command that’s already abstained, or reinstate a command
that’s already reinstated.
There is a strange set of restrictions on ABSTAIN and
REINSTATE that has existed since INTERCAL-72;
historically such restrictions have not always been implemented, or
have not been implemented properly. They together define an unusual
interaction of ABSTAIN and GIVE UP (note, for
instance, that there isn’t a gerund for GIVE UP).
The wording used in the INTERCAL-72 manual is:
[...] the statement DO ABSTAIN FROM GIVING UP is not accepted, even though DON’T GIVE UP is. [...] DO REINSTATE GIVING UP is invalid, and attempting to REINSTATE a GIVE UP statement by line label will have no effect. Note that this insures that DON’T GIVE UP will always be a "do-nothing" statement.
This restriction was not implemented at all in the only
CLC-INTERCAL version before 0.02 (i.e. version 0.01), or
in C-INTERCAL versions before 1.26. The restriction was
implemented in C-INTERCAL version 1.26 and
CLC-INTERCAL versions 0.02 and later as “GIVE
UP cannot be REINSTATED or ABSTAINED
FROM”; however, this is not strictly the same as the
definition used by INTERCAL-72 (C-INTERCAL
still uses this definition in CLC-INTERCAL compatibility
mode). The J-INTERCAL implementation of this restriction
is to make REINSTATING or ABSTAINING from a
line label that refers to a GIVE UP statement a
compile-time error, but this does not fit the INTERCAL-72
definition either. The definition adopted with version 0.27 and later
of C-INTERCAL, which is hopefully correct, is to allow
abstaining from a GIVE UP statement by line number but to
rule out the other three cases (reinstating by line number silently
fails, reinstating or abstaining by gerund is impossible because there
is no gerund).
As well as CLC-INTERCAL’s extension to
abstain/reinstate by computed line number, there is also (since version
0.25) a C-INTERCAL-specific extension to
ABSTAIN, also known as ‘computed abstain’, but
with a different syntax and different semantics. It’s written
like an ordinary ABSTAIN, but with an expression between
the words ABSTAIN and FROM, for instance:
DO ABSTAIN #1 FROM (1000) DO ABSTAIN .2 FROM WRITING IN
Unlike non-computed ABSTAIN, this form allows a command to
be abstained from even if it’s already been abstained from; so if
the first example command is run and line (1000) is already abstained,
it becomes ‘double-abstained’. The number of times the
statement is abstained from is equal to the number of times it was
already abstained from, plus the expression (whereas with non-computed
abstain, it ends up abstained once if it wasn’t abstained at all,
and otherwise stays at the same abstention status). Reinstating a
statement always de-abstains it exactly once; so double-abstaining from
a statement, for instance, means it needs to be reinstated twice before
it will actually execute.
There are many uses for ABSTAIN (both the computed and
non-computed versions) and REINSTATE, especially when
interacting with ONCE and AGAIN (see ONCE and AGAIN); the computed version, in
particular, is a major part of a particular concise way to write
conditionals and certain kinds of loops. They also play an important
role in multithreaded programs.
The READ OUT and WRITE IN commands are the
output and input commands in INTERCAL; they allow
communication between the program and its user. There was a numeric I/O
mechanism implemented in INTERCAL-72, and it (or trivial
variants) have been likewise implemented in all more modern variants.
However, it had some obvious deficiences (such as not being able to
read its own output) which meant that other methods of I/O were
implemented in C-INTERCAL and CLC-INTERCAL.
The syntax of READ OUT and WRITE IN is the
same in all cases: the name of the command followed by an
intersection-separated list of items; the form of each item, the
compiler you are using, and its command line arguments together
determine what sort of I/O is used, which can be different for
different elements in the list.
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| yes | all versions | see text | all versions |
INTERCAL-72 had its own versions of I/O commands; these
commands are available in all modern INTERCAL
compilers as well (but CLC-INTERCAL implements output
slightly differently). To distinguish INTERCAL-72 input
and output from the other more modern types of I/O, the READ
OUT and WRITE IN commands must take one of the
following values: a onespot or twospot variable, a single element of a
tail or hybrid array, or (in the case of READ OUT) a
constant, meaning that these are some examples of the possible forms:
READ OUT .1 READ OUT ;2 SUB .3:4 READ OUT #3 WRITE IN :4 WRITE IN ,5 SUB #6
The statements do what you would expect; READ OUT outputs
its argument to the user, and WRITE IN inputs a number
from the user and assigns it to the variable or array element
referenced. (If the variable, or the array that contains the array
element, happens to be read-only, the input or output still happens but
in the case of WRITE IN silently skips the assignment,
instead throwing away the input.) The formats used for input and output
are, however, different from each other and from the formats used by
most mainstream languages.
Input is achieved by writing a number in decimal, one digit at a time,
with each digit written out as a word; so to input the number 12345, a
user would have to type ONE TWO THREE FOUR FIVE as input
(if they were using English, the most portable choice of language). In
INTERCAL-72 only English is accepted as a language, but
other compilers accept other languages in addition.
C-INTERCAL from version 0.10 onwards accepts English,
Sanskrit, Basque, Tagalog, Classical Nahuatl, Georgian, and Kwakiutl;
also Volapük from version 0.11 onwards, and Latin from version 0.20
onwards. J-INTERCAL accepts the same languages, except
with Esperanto instead of Latin; from version 0.05 of
CLC-INTERCAL onwards, the same list of languages as
C-INTERCAL is supported (apart from Latin, which was added
in version 1.-94.-8), plus Scottish Gaelic.
The format that output can be read in is a modified form of Roman numerals, known as ‘butchered’ Roman numerals. INTERCAL-72, C-INTERCAL and J-INTERCAL do this the same way; CLC-INTERCAL is somewhat different. The characters ‘I’, ‘V’, ‘X’, ‘L’, ‘C’, ‘D’, and ‘M’ mean 1, 5, 10, 50, 100, 500 and 1000 respectively, placing a lower-valued letter after a higher-valued letter adds them, and placing a lower-valued letter before a higher-valued letter subtracts it from the value; so ‘XI’ is 11 and ‘IX’ is 9, for instance. In INTERCAL-72, C-INTERCAL, and J-INTERCAL, a bar over a numeral multiplies its value by 1000, and writing a letter in lowercase multiplies its value by 1000000; however, CLC-INTERCAL uses lowercase to represent multiplication by 1000 and for multiplication by 1000000 writes a backslash before the relevant numeral.
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| no | version 0.07+ | version 0.05+ | no |
C-INTERCAL’s method of character-based (rather than
numeric) input and output is known as the Turing Tape method; it is a
binary (character-set-agnostic) input/output mechanism. To specify that
C-INTERCAL-style I/O is being used, an array must be used
as the argument to READ OUT or WRITE IN; as
the syntax is the same as for CLC-INTERCAL’s I/O,
command-line arguments and the capabilities of the version of the
compiler being used serve to distinguish the two mechanisms.
The character-based input writes as many characters into a tail or
hybrid array as will fit, one character in each element. The number
that’s written into the array is not the character code, though,
but the difference between the character code and the previous
character code, modulo 256. (To be precise, the code is the new
character minus the previous character, or 256 minus (the previous
character minus the new character) if the previous character had a
higher character code; the ’previous character’ is the
previous character from the input, not the previous character written
into the array.) End-of-file causes 256 to be written into the array.
The concept is that of a circular tape containing all the characters,
where the program measures how many spaces it needs to move along the
tape to reach the next character. The ’previous character’
starts at 0, but is preserved throughout the entire program, even from
one WRITE IN to the next.
Character-based output uses a similar model, but conceptually the output device moves on the inside of the tape, rather than on the outside. Therefore, the character that is actually output is the bit-reversal of the difference between the last character output before it was bit-reversed and the number found in the array (subtracting in that order, and adding 256 if the result is negative). (Rather than trying to parse the previous sentence, you may find it easier to look either at the source code to the compiler if you have it (the relevant part is binout in src/cesspool.c) or at some example C-INTERCAL programs that do text-based I/O.)
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| no | see text | all versions | no |
There are also two CLC-INTERCAL-specific I/O mechanisms. These are Baudot-based text I/O (which is also implemented from C-INTERCAL version 0.27 onwards), and CLC-INTERCAL generalised binary I/O (not implemented in C-INTERCAL).
Baudot text-based I/O is specified by using a tail array as an argument
to WRITE IN or READ OUT. (A tail array can
also be used to specify C-INTERCAL-style Turing Tape I/O.
In order to determine which is used: both C-INTERCAL and
CLC-INTERCAL use their own sort of I/O unless a
command-line argument instructs them to use the other.) In the case of
WRITE IN, one line of input is requested from the user
(C-INTERCAL requires this to be input in Latin-1, and will
then automatically convert it; CLC-INTERCAL gives the
option of various character sets for this input as command-line
options); the final newline is removed from this line, then it is
converted to extended Baudot and stored in the tail array specified
(causing an error if the array is too small). Because Baudot is only a
5-bit character set, each element is padded to 16 bits;
CLC-INTERCAL pads with zeros, C-INTERCAL pads
with random bits. Trying to input at end-of-file will act as if the
input were a blank line. READ OUT is the reverse; it
interprets the array as extended Baudot and converts it to an
appropriate character set (Latin-1 for C-INTERCAL, or
whatever was specified on the command line for
CLC-INTERCAL), which is output to the user, followed by a
newline. Note that the Baudot is often longer than the corresponding
character in other character sets due to the need to insert shift
codes; for information on the extended Baudot character set, Character Sets.
Generalised binary I/O is specified using a hybrid array as an argument
to WRITE IN or READ OUT. Input works by
reading in a number of bytes equal to the length of the array (without
trying to interpret them or translating them to a different character
set), prepending a byte with 172 to the start, padding each byte to 16
bits with random data, then replacing each pair of consecutive bytes
(that is, the first and second, the second and third, the third and
fourth, and so on) with (the first element selected from the second
element) mingled with (the complement of the first element selected
from the complement of the second element). Output is the exact
opposite of this process. End-of-file reads a 0, which is padded with
0s rather than random data; if a non-end-of-file 0 comes in from the
data, its padding will contain at least one 1. Any
all-bits-0-even-the-padding being read out will be skipped.
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| yes | all versions | all versions | all versions |
The GIVE UP command causes the program to end (or, in a
multithreaded program, causes the current thread to end). It is written
simply as GIVE UP. There is not much else to say about it,
except to mention that it is the only way to end the program without an
error unless the last line of the program is TRY AGAIN,
and that it has an unusual interaction with ABSTAIN; for
details of this, see ABSTAIN. (Going past the
last command in the program is an error.)
There is no gerund for GIVE UP; in particular,
GIVING UP is a syntax error.
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| no | version 0.25+ | no | no |
The TRY AGAIN command is a very simple command with many
limitations; its effect is to place the entire program in a loop. If it
exists, it must be the very last command in the program (it cannot even
be followed by syntax errors), and it causes execution of the program
to go back to the first command. If the TRY AGAIN command
is abstained or for some other reason doesn’t execute when
reached, it exits the program without the error that would usually be
caused by going past the last line of code.
The gerund for TRY AGAIN is TRYING AGAIN.
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| no | see text | see text | see text |
The COME FROM statement (incidentally also invented in
1972, but not in connection with INTERCAL) is the
main control-flow command in CLC-INTERCAL (which
deprecates NEXT), and one of two main control flow
structures in other modern INTERCAL compilers. It
takes either a label or an expression as its argument; these forms are
noncomputed COME FROM and computed COME FROM.
Noncomputed COME FROM was implemented in version 0.5 of
C-INTERCAL, but did not conform to modern-day semantics
until version 0.7; it is available in every version of
CLC-INTERCAL and J-INTERCAL. Computed
COME FROM support is available in every version of
CLC-INTERCAL and in C-INTERCAL from version
0.25 onwards, but not in J-INTERCAL; the variant
NEXT FROM of COME FROM is available from
CLC-INTERCAL version 1.-94.-8 and C-INTERCAL
version 0.26 (both computed and noncomputed). C-INTERCAL
and CLC-INTERCAL also have a from-gerund form of
COME FROM and NEXT FROM, which was also
implemented from CLC-INTERCAL version 1.-94.-8 and
C-INTERCAL version 0.26.
The basic rule of COME FROM is that if a COME
FROM statement references another statement, whenever that
statement is reached, control flow will be transferred to the
COME FROM after that statement finishes executing.
(NEXT FROM is identical except that in addition to the
COME FROM behaviour, the location immediately after the
statement that was nexted from is saved on the NEXT stack, in much the
same way as if the statement being nexted from was itself a
NEXT.)
Here are examples of noncomputed, computed, and from-gerund COME
FROM:
DO COME FROM (10) DO COME FROM #2$'.1~#1' DO COME FROM COMING FROM
(The last example is an infinite loop. If it said DO NEXT FROM
NEXTING FROM, it would not be an infinite loop because the NEXT
stack would overflow and cause an error. This also establishes the
gerunds used for COME FROM and NEXT FROM.)
There are some things to be careful with involving COME
FROM and NEXT FROM. First, if the statement come
from or nexted from happens to be a NEXT, the
NEXT doesn’t count as ’finishing
executing’ until the NEXT stack entry created by the
NEXT is RESUMEd to. In particular, this means
that if FORGET is used to remove the entry, or a
RESUME with a large argument resumes a lower entry, the
COME FROM doesn’t steal execution at all.
Second, you may be wondering what happens if two COME
FROMs or NEXT FROMs aim at the same line. In a
non-multithreaded program (whether a program is multithreaded or not is
determined by a compiler option for those compilers that support it),
this is an error; but it is only an error if the statement that they
both point to finishes running, and both COME FROMs or
NEXT FROMs try to execute as a result (they might not if,
for instance, one is abstained or has a double-oh-seven causing it not
to run some of the time). If both COME FROMs or NEXT
FROMs are noncomputed, however, a compiler can (but does not
have to) give a compile time error if two COME FROMs or
NEXT FROMs share a label, and so that situation should be
avoided in portable code. (If it is wanted, one solution that works for
C-INTERCAL and CLC-INTERCAL is to use
computed COME FROMs or NEXT FROMs with a
constant expression.)
Some programming support libraries may be included automatically at the end of your program by the C-INTERCAL compiler. While such a convenience feature might be judged not in the spirit of INTERCAL, the required level of perversity is arguably restored by the way inclusion is triggered: whenever your program refers to a line from specified magic ranges without defining any line in those ranges in the program.
(CLC-INTERCAL does not have this feature, but it is trivial to concatenate a copy of any desire library onto the end of the program.)
The following table maps magic line ranges to systen libraries. Descriptions of the libraries follow it.
| From | To | Versions | Description |
|---|---|---|---|
| (1000) | (1999) | All | Basic System Library |
| (5000) | (5999) | >=0.29 | Floatring Point Library |
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| yes | all versions | no | all versions |
INTERCAL has a system library, called ‘syslib’ (versions for bases other than 2 will have a numeric suffix on the name).
The intention of the system library is to provide a range of useful
capabilities, like multiplication, that can otherwise be hard to write
in INTERCAL. System library routines are used by
NEXTING to their line number (see NEXT), where they will make changes to certain variables
depending on certain other variables (depending on which routine is
called), and RESUME back to the original program. As the
system library is itself written in INTERCAL, there
are some restrictions that need to be obeyed for calls to it to be
guaranteed to work; none of the variables it uses (.1 to
.6 and :1 to :5) should be
read-only or overloaded (although the value of any variables that
aren’t mentioned in the routine’s description will be
preserved by the routine), and none of the lines in it should have
their abstention status changed by lines outside it (this can happen
with blatant infractions like DO ABSTAIN FROM (1500) or
more subtle problems like gerund-abstention) or have COME
FROMs or NEXT FROMs aiming at them.
The system library is currently available in all bases from 2 to 7 (see TriINTERCAL), but not every command is available in every base, and C-INTERCAL is the only one of the three compilers listed above that has the system library to ship with a version in bases other than 2. (This table was originally based on the INTERCAL-72 manual, but has had extra information added for bases other than 2.) Here, “overflow checked” means that #1 is assigned to .4 if there is not an overflow, and #2 is assigned to .4 if there is; “overflow captured” means that if there is overflow, the digit that overflowed is stored in the variable referenced. In all cases, division by 0 returns 0.
| Line | Description | Bases |
|---|---|---|
| (1000) | .3 <- .1 plus .2, error exit on overflow | 2, 3, 4, 5, 6, 7 |
| (1009) | .3 <- .1 plus .2, overflow checked | 2, 3, 4, 5, 6, 7 |
| (1010) | .3 <- .1 minus .2, no action on overflow | 2, 3, 4, 5, 6, 7 |
| (1020) | .1 <- .1 plus #1, no action on overflow | 2, 3, 4, 5, 6, 7 |
| (1030) | .3 <- .1 times .2, error exit on overflow | 2, 3, 4, 5, 6, 7 |
| (1039) | .3 <- .1 times .2, overflow checked | 2, 3, 4, 5, 6, 7 |
| (1040) | .3 <- .1 divided by .2 | 2, 3, 4, 5, 6, 7 |
| (1050) | .2 <- :1 divided by .1, error exit on overflow | 2, 3, 4, 5, 6, 7 |
| (1200) | .2 <- .1 times #2, overflow captured in .3 | 4, 6 |
| (1210) | .2 <- .1 divided by #2, one digit after the quartic or sextic point stored in .3 | 4, 6 |
| (1500) | :3 <- :1 plus :2, error exit on overflow | 2, 3, 4, 5, 6, 7 |
| (1509) | :3 <- :1 plus :2, overflow checked | 2, 3, 4, 5, 6, 7 |
| (1510) | :3 <- :1 minus :2, no action on overflow | 2, 3, 4, 5, 6, 7 |
| (1520) | :1 <- .1 concatenated with .2 | 2, 3, 4, 5, 6, 7 |
| (1530) | :1 <- .1 times .2 | 2, 3, 4, 5, 6, 7 |
| (1540) | :3 <- :1 times :2, error exit on overflow | 2, 3, 4, 5, 6, 7 |
| (1549) | :3 <- :1 times :2, overflow checked | 2, 3, 4, 5, 6, 7 |
| (1550) | :3 <- :1 divided by :2 | 2, 3, 4, 5, 6, 7 |
| (1700) | :2 <- :1 times #2, overflow captured in .1 | 4, 6 |
| (1710) | :2 <- :1 divided by #2, one digit after the quartic or sextic point stored in .1 | 4, 6 |
| (1720) | :2 <- :1 times the least significant digit of .1, overflow captured in .2 | 5, 7 |
| (1900) | .1 <- uniform random number from #0 to #65535 | 2, 3, 4, 5, 6, 7 |
| (1910) | .2 <- normal random number from #0 to .1, with standard deviation .1 divided by #12 | 2, 3, 4, 5, 6, 7 |
If you happen to be using base 2, and are either using the external call system (see External Calls) or are willing to use it, it is possible to use a version of the system library written in C for speed, rather than the default version (which is written in INTERCAL). To do this, use the command line options -eE (before the INTERCAL file), and syslibc (at the end of the command line).
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| yes | all versions | no | all versions |
INTERCAL also has a floating-point library, called ‘floatlib’, presently available only in base 2. It is used by several of the demonstration programs shipped with the distribution. In versions after 0.28 it is included automatically at the end of your program by the compiler whenever your program refers to a line from (5000) to (5999) without defining any line in that range in the program.
Here is a summary of routines in floatlib.i:
| Line | Description |
|---|---|
| (5000) | :3 <- :1 plus :2 |
| (5010) | :3 <- :1 minus :2 |
| (5020) | :2 <- the integer part of :1, :3 <- the fractional part of :1 |
| (5030) | :3 <- :1 times :2 |
| (5040) | :3 <- :1 divided by :2 |
| (5050) | :3 <- :1 modulo :2 |
| (5060) | :2 <- :1 cast from a two’s-complement integer into a floating-point number |
| (5070) | :2 <- :1 cast from a floating-point number into the nearest two’s-complement ineger |
| (5080) | :2 <- :1 cast from a floating-point number into a decimal representation in scientific notation |
| (5090) | :2 <- :1 cast from a decimal representation in scientific notation into a floating-point number |
| (5100) | :2 <- the square root of :1 |
| (5110) | :2 <- the natural logarithm of :1 |
| (5120) | :2 <- e to the power of :1 (the exponential function) |
| (5130) | :3 <- :1 to the power of :2 |
| (5200) | :2 <- sin :1 |
| (5210) | :2 <- cos :1 |
| (5220) | :2 <- tan :1 |
| (5400) | :1 <- uniform random number between zero and one exclusive |
| (5410) | :2 <- :1 times phi |
| (5419) | :2 <- :1 divided by phi |
Note: All of the above routines except (5020), (5060), (5080), (5200), (5210), and (5400) also modify .5 as follows: .5 will contain #3 if the result overflowed or if the arguments were out of domain, #2 if the result underflowed, #1 otherwise. (See below.)
The INTERCAL floating-point library uses the IEEE format for 32-bit floating-point numbers, which uses bit 31 as a sign bit (1 being negative), bits 30 through 23 hold the exponent with a bias of 127, and bits 22 through 0 contain the fractional part of the mantissa with an implied leading 1. In mathematical notation:
‘N = (1.0 + fraction) * 2^(exponent - 127) * -1^sign’
Thus the range of floating-point magnitudes is, roughly, from 5.877472*10^-39 up to 6.805647*10^38, positive and negative. Zero is specially defined as all bits 0. (Actually, to be precise, zero is defined as bits 30 through 0 as being 0. Bit 31 can be 1 to represent negative zero, which the library generally treats as equivalent to zero, though don’t hold me to that.)
Note that, contrary to the IEEE standard, exponents 0 and 255 are not given special treatment (besides the representation for zero). Thus there is no representation for infinity or not-a-numbers, and there is no gradual underflow capability. Conformance with widely-accepted standards was not considered to be a priority for an INTERCAL library. (The fact that the general format conforms to IEEE at all is due to sheer pragmatism.)
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| no | version 0.7+ | version 1.-94.-8+ | no |
One extension to INTERCAL that is implemented by both C-INTERCAL and CLC-INTERCAL is known as TriINTERCAL, and extends INTERCAL to bases other than binary. Unlike ordinary INTERCAL programs, which have the extension ‘.i’, TriINTERCAL programs in bases from 3 to 7 (the only allowed bases) have extensions from ‘.3i’ to ‘.7i’ respectively.
The change of numeric base only affects expressions, and in particular the behaviour of operators, and the range of variables. (The onespot and twospot ranges become the highest number of trits or other digits in the base required that fit inside the binary ranges, so for instance, the maximum value of a onespot variable in ternary is 59048, or 3 to the power 10 minus 1.) Interleave/mingle is the simplest to explain; it alternates digits just as it alternated bits in binary. The other operators all change, as follows:
? and ^). (In Princeton
syntax, these are the bookworm or yen sign, and a spike
(|).) The two operators do the same thing in binary, but
differ in higher bases. (Nevertheless, it is an error to use a sharkfin
in binary, because it is a so-called ‘controlled unary
operator’, as are the rest of the new operators defined in this
section, which has a lower limit on which base it is allowed in.)
Instead of doing the exclusive-or operation, the bits being combined
are either subtracted or added; if the result is out of range for the
base being used, the base is added or subtracted from the result until
it is in range. (For the subtraction, the bit that was less significant
is subtracted from the bit that was more significant in any given pair
of bits, except for the subtraction between the most and least
significant bits, where the most significant bit is subtracted from the
least.)
The way to think of it is this: in base 2, an AND gives the result
0 if either argument is a 0, and otherwise a 1, and likewise, an OR
gives the result 1 if either argument is a 1, and otherwise a 0;
they could be said to favour 0 over 1 and 1 over 0 respectively. In
base 3, AND favours 0 over 2 over 1, OR favours 2 over 1 over 0,
and BUT favours 1 over 0 over 2. (The symbol for BUT is
@ (a ‘whirlpool’, which is another name
for the BUT operation) in Atari syntax, and ? in
Princeton syntax.) The pattern continues: in base 4, AND favours 0
over 3 over 2 over 1, BUT favours 1 over 0 over 3 over 2, 2BUT
(written 2@ or 2?) favours 2 over 1 over
0 over 3, and OR favours 3 over 2 over 1 over 0. (This can be
extended to higher bases following the same pattern, introducing
operators 3@ or 3?, etc., to favour 3,
etc., when neither AND (which always favours 0) nor OR (which
favours the highest digit in the base) are available.) All the
whirlpool operators are controlled unary operators, which are only
legal when both the base contains the favoured digit, and they
aren’t redundant to AND nor OR.
Note that the base doesn’t affect anything other than variable ranges and expressions; in particular, it doesn’t affect the bit-reversal used by Turing Tape I/O. (The tape still has characters written on it in binary, even though the program uses a different base.)
The multithreading and backtracking extensions to
INTERCAL were originally invented by Malcom Ryan,
who implemented COME FROM-based multithreading as a
modified version of C-INTERCAL, known as Threaded
INTERCAL, but did not implement backtracking. (The
same functionality is implemented in C-INTERCAL today, but
with different code. Most likely, this means that the original code was
better.) He also invented the original version of Backtracking
INTERCAL, but did not implement it; the only known
implementation is the C-INTERCAL one. A different version
of multithreading, using WHILE, was implemented as part of
CLC-INTERCAL (like all extensions first available in
CLC-INTERCAL, it is most likely due to Claudio Calvelli)
and then added to C-INTERCAL, although its implications
were not noticed for some time afterwards.
So nowadays, three freely-mixable threading-like extensions to INTERCAL exist, all of which are implemented in C-INTERCAL. (A fourth, Quantum INTERCAL, is implemented in CLC-INTERCAL but not C-INTERCAL, and so will not be discussed further here.) If you’re wondering about the description of backtracking as a threading-like extension, it’s implemented with much of the same code as multithreading in C-INTERCAL, because the INTERCAL version can be seen as roughly equivalent to multithreading where the threads run one after another rather than simultaneously. (This conceptualisation is probably more confusing than useful, though, and is also not strictly correct. The same could probably be said about INTERCAL as a whole, for that matter.)
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| no | version 0.25+ | version 0.05+ | no |
The original multithreading implementation worked by giving a new
meaning to what was previously an error condition. If in a
multithreaded program (a program is marked as multithreaded using
options to a compiler) two or more COME FROMs or
NEXT FROMs (or a mixture of these) attempt to steal
control simultaneously, the original thread splits into multiple
threads, one for each of the commands trying to take control, and a
different command gains control of the program in each case.
From then on, all the threads run simultaneously. The only thing shared
between threads (apart from the environment in which they run) is the
abstained/reinstated status of each command; everything else is
separate. This means, for instance, that it’s possible to change
the value of a variable in one thread, and it will not affect the
corresponding variable in other threads created this way. Likewise,
there is a separate NEXT stack in each thread; if both a COME
FROM and a NEXT FROM aim at the same line, for
instance, the NEXT FROM thread will end up with a NEXT
stack entry that isn’t in the COME FROM thread,
created by the NEXT FROM itself. This is known as unwoven
thread creation; none of the threads created this way are
‘woven’ with any of the other threads created this way.
(Whether threads are woven depends on how they were created.) If the
thread being split was itself woven with other threads, exactly one of
the resulting threads after the split is woven with the threads that
the original thread was woven to, but the rest will not be woven to
anything. (If that seems a somewhat unusual rule: well, this is
INTERCAL.)
In C-INTERCAL, there are other guarantees that can be made
about unwoven threads (that is, threads not woven to any other thread).
In particular, they can all be guaranteed to run at approximately the
same speed; to be more precise, the number of commands that have been
given the chance to execute in any given thread will not differ by more
than 2 from the number of commands that have been given the chance to
execute in any other thread that was created at the same time.
(However, COME FROMs and NEXT FROMs can make
this relationship less precise; it is unspecified (in the technical
sense that means the compiler can choose any option it likes and change
its mind on a whim without telling anyone) whether a COME
FROM or NEXT FROM aiming at the current command
counts towards the command total or not, thus causing the relationship
to become weaker the more of them have the chance to execute. In
versions of C-INTERCAL from 0.27 onwards, there is a third
guarantee; that if a COME FROM comes from itself, it will
actually give other threads at least some chance to run, at some speed,
by counting itself as a command every now and then; previously this
requirement didn’t exist, meaning that a COME FROM
could block all threads if it aimed for itself due to the speed
restrictions and the fact that COME FROMs need not count
towards the total command count.) Also, all commands, including any
ONCE or AGAIN attached to the command, are
atomic; this means that it’s impossible for another thread to
conflict with what the command is doing. (In a departure from the usual
INTERCAL status quo, these guarantees are somewhat
better than in most other languages that implement threading,
amusingly continuing to leave INTERCAL with the
status of being unlike any other mainstream language.)
The only way to communicate between unwoven threads is by changing the
abstention status of commands; this always affects all threads in the
program, whether woven or not. (The combination of ABSTAIN
and ONCE is one way to communicate atomically, due to the
atomic nature of ONCE.)
If there are at least two threads, the GIVE UP command
ends the current thread, rather than the current program.
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| no | version 0.27+ | version 0.05+ | no |
The WHILE command (which is not strictly speaking a
command, but more a sort of metacommand that joins commands) is a
second method of achieving multithreading. (In
CLC-INTERCAL, there are at least two other meanings for
WHILE, but only the one implemented in
C-INTERCAL is discussed here.) The syntax is somewhat
unusual, and consists of two commands separated by the
WHILE keyword, but sharing the statement identifier,
execution chance, and any ONCE/AGAIN keyword
that may be present. For instance:
(1) DO COME FROM ".2~.2"~#1 WHILE :1 <-
"'?.1$.2'~'"':1/.1$.2'~#0"$#65535'"$
"'"'&.1$.2'~'#0$#65535'"$#0'~#32767$#1"
(OK, maybe that’s an unnecessarily complicated example, and maybe
it shouldn’t have included the / operator which is
part of another INTERCAL extension (see Operand Overloading). Still, I thought that
maybe you’d want to see how addition can be implemented in
INTERCAL.)
A WHILE command starts two threads (the original thread
that ran that command and a new one), one of which runs the command to
the left of the WHILE and one of which runs the command to
the right. Any line number applies to the left-hand command, not the
WHILE as a whole, which is a metalanguage construct. NEXTING
FROM, ABSTAINING FROM or similar behaviour with
respect to the WHILE itself is impossible, although
it’s certainly possible to abstain from either of its operands
(and abstaining from the left operand has much the same effect as
abstaining from the WHILE itself; the right-hand thread
deliberately takes a bit of time to get started just so that this
behaviour happens). The right-command thread starts just before the
left command is run (so NEXTING, etc., directly to the
left command will not start that loop in the first place); if that
command finishes (which may be almost immediately for something like a
calculate command, or take a long time for something like
NEXT), that thread loops and reruns that command as long
as the left command has not finished; COMING FROM that
command, or a NEXT/NEXT FROM from/aiming at
that command, doesn’t count as finishing that command until it is
RESUMEd back to (if possible; if it’s come from,
that command can never end and the right-hand loop will continue
forever, or until it GIVEs UP or the loop
ends due to the command ending later in another thread). A
WHILE command itself exists across all threads of a
multithreaded program in a way; for each left-hand command that ends
(in any thread), the next time a right-hand command of the same
WHILE ends it will cause the thread it’s looping in
to end, regardless of whether that thread corresponds to the thread in
which the left-hand command ended. (As well as a right-hand command
ending, there’s also the possibility that it never got started;
there is a delay before the right-hand command runs during which a
left-hand command ending can prevent the right-hand thread starting in
the first place; this counts as the same sort of event as terminating a
right-hand loop, and can substitute for it anywhere a right-hand
command ending is mentioned.) There is one exception, in that if two or
more left-hand commands end in a space of time in which no right-hand
commands for that WHILE ends, they together only cause one
right-hand command to end. (What, did you expect the logical and
orthogonal behaviour?)
The two threads produced by a WHILE (the original thread
and a new copy of it) have more in common than ordinary
INTERCAL threads created by COME FROM;
ordinary threads share only ABSTAIN/REINSTATE
information, whereas the WHILE-produced threads count as
‘woven’ threads which also share variables and stashes.
(They still have separate instruction pointers, separate instruction
pointer stacks, such as the NEXT stack, and separate choicepoint lists.
Overloading information is shared, though.) Being woven is a
relationship between two or more threads, rather than an attribute of a
thread, although a thread can be referred to as being unwoven if it is
not woven to any other thread.
Ordinary multithreading cannot create woven threads. When threads are
created by multiple COME FROMs from an original thread,
which was woven with at least one other thread, one of the resulting
threads counts as the ‘original’ thread and remains woven;
the rest are ‘new’ threads which initially start out with
the same data as the original, but are not woven with anything.
Backtracking in a thread (see Backtracking)
causes it to unweave with any threads it may be woven with at the time
(so the data in the thread that backtracks is set back to the data it,
and the threads it was woven with at the time, had at the time of the
MAYBE, but the other threads continue with the same data
as before). The only way to cause three or more threads to become woven
is with a new WHILE inside one of the threads that is
already woven, which causes all the new threads to be woven together
(the weaving relationship is transitive).
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| no | version 0.25+ | no | no |
A somewhat unusual threading construct that’s available is
backtracking. In case you haven’t come across it before (the
concept exists in other languages but is implemented differently and
usually in a less general way), the basic idea is that instead of
executing or not executing a command, you can MAYBE
execute a command. This causes the command to be executed, but also
creates a dormant thread in which the command wasn’t executed; at
any time later, the program can either decide that it liked the
consequences of the command and GO AHEAD and get rid of
the dormant thread, or decide that it didn’t like the consquences
of the command and GO BACK to the dormant thread,
discarding the current one. The dormant thread is more commonly called
a ‘choicepoint’, that is, a point at which a choice was
made but a different choice can still be made, and is generally not
thought of as a thread at all by most programmers. (In case
you’re wondering: dormant threads are always unwoven.)
To create a choicepoint, the statement identifier MAYBE is
used, rather than the more usual DO or
PLEASE. (Combination statement identifiers are still
allowed, but must be in the order MAYBE PLEASE DO NOT with
optionally some parts omitted, or different versions of
NOT used, or both.) Here’s an example:
MAYBE DON'T GIVE UP
When a command whose statement identifer contains MAYBE is
reached, it is executed or not executed as normal, but in addition a
choicepoint is created containing the program as it is at that time.
Only ABSTAIN and REINSTATE, which always
affect all threads in a program (even choicepoints), can alter the
values stored in the choicepoint; so in this way, a choicepoint is also
somewhat similar to the concept of a continuation in other languages.
The choicepoint is placed on a choicepoint stack, which is maintained
separately for each thread in much the same way that stashes and the
NEXT stack are.
The choicepoint does not actually do anything immediately, but if the
program doesn’t like the look of where it’s ended up, or it
decides to change its mind, or just wants to try all the possibilities,
it can call the GO BACK command (which has no arguments,
and is just the statement identifier, optional execution chance,
GO BACK, and optional ONCE or
AGAIN). This causes the current thread to unweave from all
other threads and then replace itself with the thread created by the
choicepoint on top of the choicepoint stack. The difference is that
this time, the abstention or reinstatement status of the command that
was modified with MAYBE is temporarily reversed for
determining whether it runs or not (this reversal only lasts
immediately after the GO BACK, and does not affect uses of
the command in other threads or later in the same thread), so unless it
has been ABSTAINed or REINSTATEd in the
meantime it will run if and only if it wasn’t run the first time.
The choicepoint stack’s top entry is replaced by a
‘stale’ choicepoint that definitely isn’t a thread;
attempting to GO BACK to a stale choicepoint instead
causes the stale choicepoint to be deleted and the program to continue
executing. (This is what gives INTERCAL’s
backtracking greater flexibility in some ways than some other
languages; to get backtracking without the stale choicepoints having an
effect, simply run COME FROM the GO BACK as
the previous statement.)
Note that, though, when a thread splits into separate threads (whether
woven or unwoven), the choicepoint stack doesn’t split
completely, but remains joined at the old top of stack. The two
choicepoint stacks can add and remove items independently, but an
attempt to GO BACK to before the current thread split off
from any other threads that are still running instead causes the
current thread to end, although it will GO BACK as normal
if all other threads that split off from it or that it split off from
since the top choicepoint of the stack was created have ended since.
This means that it’s possible to backtrack past a thread
splitting and get the effect of the thread unsplitting, as long as both
resulting threads backtrack; this is another way in which
INTERCAL’s backtracking is more flexible than
that of some other languages.
If, on the other hand, a program decides that it likes where it is and
doesn’t need to GO BACK, or it wants to GO
BACK to a choicepoint lower down the stack while skipping some
of the ones nearer the top of the stack, it can run the GO
AHEAD command, which removes the top choicepoint on the stack,
whether it’s a genuine choicepoint or just a stale one.
Both GO AHEAD and GO BACK cause errors if an
attempt is made to use them when the choicepoint stack is empty.
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| no | version 0.26+ | version 0.05+ | no |
(Operand overloading in C-INTERCAL is nowhere near as advanced as it is in CLC-INTERCAL. This chapter only explains the partial implementation used by C-INTERCAL; for a full implementation, see CLC-INTERCAL and its documentation.)
Operand overloading is a method of using a onespot or twospot variable as a substitute for an expression. When a variable is overloaded to an expression (which could be another variable, or something more complex), any uses of that variable cause the expression to be substituted instead.
At the beginning of the program, all variables stand for themselves; so
.1 really does mean .1, for instance. The
meaning of a variable can be overloaded using the slat operator
(/), which is the same in both Princeton and Atari syntax:
it is a binary operator whose left argument must be a onespot or
twospot variable and whose right argument can be any expression. The
slat operator returns the true value of its left argument, but as a
side effect, changes the meaning of its left argument to be its right
argument. Here is an example:
DO .1 <- .2/'.3~.4'
The example causes .2’s true value to be assigned to
.1 (unless of course .1 is read-only), but
also causes .2 from then on to actually mean
'.3~.4', except when it’s the left operand of a slat
operator. So for instance, DO .1 <- .2 would actually
assign '.3~.4' to .1. Somewhat confusingly,
this also works in the other direction; DO .2 <- .1
would assign .1 to '.3~.4', which would have
the effect of changing the values of .3 and
.4 so that '.3~.4' had the correct value, or
throw an error if it couldn’t manage this. (The general rule in
this case is that any variable or constant in the expression that
overloads the variable is at risk of being changed; this is known as a
‘reverse assignment’. Code like DO .1 <-
.1/#1 is entirely capable of changing the value of
#1, although to protect new INTERCAL
users C-INTERCAL will refuse to carry out operations that
change the value of constants unless a command-line switch (see
-v) is used to give it permission. In
C-INTERCAL, changing the value of a constant only changes
meshes with that value, but in CLC-INTERCAL it can also
change non-mesh uses of that constant, so doing so is not portable
anyway.)
When multiple overloading rules are in effect, they are all applied;
overloading .1 to '.2~.3' and .2
to '.3$.4' will cause .1 to refer to
''.3$.4'~.3'. However, this expansion stops if this would
cause a loop; to be precise, overloading is not expanded if the
expansion is nested within the same expansion at a higher level (so
.1/.2 and .2/.1 together cause
.1 to expand to .2, which expands to
.1, which cannot expand any further). In
C-INTERCAL, the expression on the right hand side of a
slat is not evaluated and not expanded by operand overloading.
STASHING a variable causes its overloading information to
be stashed too; RETRIEVING it causes its overload rule to
also be retrieved from the stash (or any overload rule on the variable
to be removed if there wasn’t one when the variable was stashed).
Overloading a onespot variable to a twospot variable or vice versa is possible, but the results are unlikely to be predictable, especially if a onespot variable is used to handle a twospot value. Possible outcomes include truncating the value down to the right bitwidth, throwing an error if a value outside the onespot range is used, and even temporarily handling the entire twospot value as long as it doesn’t end up eventually being assigned a value greater than twospot.
Note that reverse assignments can cause unpredictable behaviour if an
attempt is made to reverse-assign the same variable twice in the same
expression. In particular, sequences of commands like DO .1 <-
.2/'.3$.3' DO .2 <- #6 are liable to succeed assigning
garbage to .3 rather than failing as they ought to do, and
likewise any situation where a variable is reverse-assigned twice in
the same expression may assign garbage to it. This behaviour is seen as
unsatisfactory, though, and plans exist to improve it for future
versions.
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| no | version 0.26+ | no | no |
PIC-INTERCAL is a simplified version of INTERCAL designed especially for embedded systems, designed to minimise code and data usage by INTERCAL programs so that they can fit on devices whose memory is measured in bytes rather than megabytes. (It is named after the first microcontroller for which code was successfully generated, and which influenced the choices of commands, the PIC16F628 manufactured by Microchip, and is most likely to be portable to other microcontrollers in the same range.) C-INTERCAL only compiles as far as C code when producing PIC-INTERCAL; it is up to the user to find the appropriate cross-compiler to translate this C into the relevant dialect of machine code. (Two header files in the distribution, src/pick1.h and src/pick2.h, don’t have any effect on the compiler but are referenced by the generated code, and the intent is for the user to change them to suit the behaviour of the PIC compiler used, because these are not as standardised as C compilers for everyday systems.)
There are several restrictions on PIC-INTERCAL programs:
ABSTAIN and REINSTATE still work, but
cannot be computed ABSTAINs, and will not necessarily
work when used to affect the system library or calls to it.
READ OUT and WRITE IN don’t work.
(See below for a replacement.)
COME FROM and NEXT FROM must aim at a
label, not an expression or gerund.
In order to provide I/O capabilities, a new command PIN is
available. It controls up to 16 I/O pins on the PIC or other embedded
system; an I/O pin is capable of receiving or sending voltages to an
electrical or electronic circuit. This explanation assumes that the
device being controlled is a PIC16F628A, and therefore has its pins in
two blocks of 8 named ‘PORTA’ and
‘PORTB’; for other microcontrollers, adapting
the code in src/pick1.h is likely to be necessary to tell
the compiler how to control the I/O pins, and the way in which this
done will affect which I/O pins it is that the program will end up
being able to communicate with.
The PIN command takes one twospot variable as its
argument, like this:
DO PIN :2
The twospot variable is conceptually divided into 4 blocks of 8 bits.
The highest two blocks control the directions of the pins in
PORTB (most significant block) and PORTA
(second most significant block); a 1 on any bit means that the
corresponding I/O pin should be set to send data, and a 0 means that it
should be set to receive data. The lower two blocks control the values
on the pins that are sending (and are ignored for receiving pins); the
second least significant block controls PORTB and the
least significant block controls PORTA, with a 1 causing
the program to set the output voltage to that of the
microcontroller’s negative voltage supply rail, and a 0 causing
the program to set the output voltage to that of the
microcontroller’s positive voltage supply rail. (These voltages
may vary on other systems; consult your system’s datasheet and
the changes you made to the header files.) After setting the pins, the
PIN command then reads them as part of the same operation,
this time setting the values of the lower blocks that are receiving,
rather than setting the pins from the lower blocks that are sending.
However, 1 and 0 bits on all bits of the twospot variable have the
opposite meaning when doing this, so that 1 means receiving/positive
voltage rail and 0 means sending/negative voltage rail. There is no way
to input without output, or vice versa, but it’s trivial to just
send the same output again (which has no effect, because the voltage on
sending pins is maintained at the same level until it is changed), or
to ignore the input received.
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| no | version 0.28+ | see text | no |
The CREATE command allows the creation of new syntax at
runtime. CLC-INTERCAL has had such a command since
1.-94.-8, but its syntax is completely different and incompatible with
the C-INTERCAL version, and so is not documented here (see
the CLC-INTERCAL documentation for more details). The
C-INTERCAL version is only defined if the -a
option is used on the command line (and a runtime error E000
otherwise), because it forces the operand overloading code to be
introduced and so slows down every variable access in the program.
The syntax of the CREATE command is to write
CREATE, then a line label, then anything. OK, well not
quite anything; you’re restricted to syntax that is supported by
the ‘just-in-case’ compiler that runs on comments at
compile time just in case they gain a meaning later (see below). The
anything provides an example statement to CREATE;
statements which look the same (but may differ in details) are created.
Typical syntax for a CREATE statement would therefore look
something like this:
DO CREATE (5) SWITCH .1 WITH .2
There is also computed CREATE, working identically to
ordinary CREATE except that the line number is taken from
an expression and the created command must start with a letter (to
avoid an ambiguity if the expression giving the line label happens to
be an array reference), with a syntax like this:
DO CREATE .5 SWITCH .1 WITH .2
Here, a new SWITCH WITH statement (there is no such
statement in INTERCAL normally) is being created.
This command makes it possible to do this:
DO SWITCH .3 WITH .4
Normally that line would be an error (E000) due to being unrecognised,
but having been CREATEd, it’s now a real statement.
(The gerund to affect created statements is COMMENT, just
like before they were created; the gerund to affect CREATE
itself is CREATION (CREATING is also allowed,
but not as elegant).) When the created statement is encountered, it
NEXTs to line (5), the line number specified in the
CREATE statement. In order for the code there to be able
to affect the variables mentioned in the statement, the variables
:1601 (for the first variable or expression mentioned),
:1602 (for the second variable or expression mentioned),
and so on, are STASHed and then overloaded to the
respective expressions or variables mentioned in the created command;
so :1601 has been overloaded to mean .3 and
:1602 has been overloaded to mean .4 at this
point. Then, the code at (5) runs; if it returns via a RESUME
#1, :1601 and :1602 will be
RETRIEVEd automatically and the program will continue from
after the created statement. (If you do not resume to that point, say
if you’re creating a flow control statement, you’ll have to
deal with the stashes for the 1600-range variables yourself.)
So what syntax is available in created statements? All the capital
letters except ‘V’ (which is an operator in
INTERCAL) are available and can be used freely and
as many times as desired; they match themselves literally. However,
they are not allowed to spell an INTERCAL keyword at
any point (so watch out for DO and FROM, for
instance). Whitespace is allowed, but is ignored (both in the
CREATE template statement, and in the code being created;
so DO SW ITCH :8 WITH :50 will also have been created).
Then, there are three groups of matchable data: scalar variables
(onespot or twospot variables, as used in the examples above) match
other scalar variables, array elements (like ,4 SUB
'.5~.6') match other array elements, and other expressions match
other other expressions. Two matchable data may not appear
consecutively in a created command, but must be separated by at least
one capital letter (to prevent array-subscript-related ambiguities;
remember that the just-in-case compiler has to compile these statements
at compile time without knowing what they are). The actual expressions
used in the CREATE statement don’t matter;
they’re just examples for the runtime to match against.
It is also possible (from C-INTERCAL version 0.29 onwards) to create new operators. Such operators are always binary operators (that is, they take two arguments and parse like mingle or select), and always return 32-bit results. There are three types of legal names for such operators, all of which are treated equivalently: lowercase letters, punctuation marks otherwise unused in INTERCAL, and overstrikes consisting of a character, a backspace, and another character (apart from overstrikes already used for built-in INTERCAL operators). The syntax for creating an operator looks like one of these:
DO CREATE (5) x DO CREATE .5 =
The arguments to the operator will be overloaded onto :1601 and :1602
(which are, like with CREATEd statements, stashed before
the overloading happens), and the return value is read from :1603
(which is stashed, then overloaded to itself). All these three
variables are retrieved again after the operator finishes evaluating.
Note that it is a very unwise idea to use a CREATEd
operator in the expression for a computed COME FROM or
NEXT FROM, because this always leads to an infinite
regress; whenever any line label is reached (including the line label
that the CREATE statement pointed at), the expression
needs to be evaluated in order to determine whether to COME
FROM that point, which in turn involves evaluating lines which
have labels.
Some other points: a newer CREATE statement supercedes an
older CREATE statement if they give equivalent templates,
multiple CREATE statements may aim at the same line (this
is the recommended technique for creating a statement that can handle
expressions even if they’re array elements or variables; you do
this by specifying multiple templates in multiple CREATE
statements), and strange things happen if a twospot variable in the
1600-range is used as an argument to a created statement itself
(because of the stash/retrieve, such a variable can usually be read,
but may not always be able to be written without the data being lost).
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| no | version 0.28+ | no | no |
C-INTERCAL has a feature allowing INTERCAL and non-INTERCAL code to be mixed. This is achieved by causing the non-INTERCAL programs to participate in the INTERCAL line-numbering model. The same feature allows expansion libraries to be linked into the code.
To create a combined program containing INTERCAL and
non-INTERCAL code, use ick as the
compiler as normal, but specify both the INTERCAL
and non-INTERCAL source files on the command line,
and use the -e command-line option. ick will
invoke other compilers as necessary, after modifying the source files
accordingly. At present, external calls are only supported to and from
C and Funge-98.
In each case, it will be the INTERCAL program that
is invoked first. (This means that it is impossible to link together
more than one INTERCAL program, but you probably
don’t want to, because concatenating the programs is likely to
have a similar effect.) You can get the INTERCAL
program to NEXT to the non-INTERCAL
program immediately, or the non-INTERCAL program to
COME FROM or NEXT FROM the
INTERCAL program immediately, to obtain the effect
of running the non-INTERCAL program first.
Note that external calls are incompatible with PIC-INTERCAL and with
multithreading; note also that you must use gcc as your
compiler, and GNU cpp and ld, for them to work in
the current version of C-INTERCAL.
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| no | version 0.28+ | no | no |
Linking C and INTERCAL programs is achieved by
placing various constructs into the C programs that are equivalent to
various INTERCAL constructs. It is possible to
simulate a line with a label and a dummy command (which serves as a
COME FROM suckpoint and NEXT target), a
command with a line label, NEXT, RESUME, and
FORGET, and COME FROM and NEXT
FROM. Onespot and twospot variables are accessible from inside
the C program, where they can be read and written; however, the
INTERCAL program cannot access any variables inside
the C program that weren’t part of the
INTERCAL program originally.
To prevent various logical impossibilities, there are restrictions on where these can be used and what preparation is needed before they are used. Also, the semantics are not always exactly what you might expect for technical reasons.
It should be observed that the INTERCAL link
intrudes on the user namespace. To prevent possible namespace clashes,
no identifiers starting with ick_ or ICK_
should be used anywhere in the linked C program for any reason, except
where specified in this manual.
For a C program to be connected to an INTERCAL program, it needs to be marked with the correct header file, and needs to have functions marked for communication with the INTERCAL program.
#include <ick_ec.h>
The header file ick_ec.h must be included using the
preprocessor in any file which uses any of the
INTERCAL external call functions, variables, or
macros. (Note that this file may not necessarily exist, or exist in
the usual place; ick will deal with making sure the
correct header file is included.) This will include
stdint.h (a standard C header file, which must exist
on your system), so that you can access INTERCAL
variables (the INTERCAL types onespot, twospot,
tail, hybrid correspond to the C types uint16_t, uint32_t,
uint16_t*, uint32_t* respectively); also, it will provide the
prototypes for all the functions and definitions for all the macros
needed to use the external calls system with C.
ICK_EC_FUNC_START
ICK_EC_FUNC_END
Many of the INTERCAL interface macros
(ick_linelabel, ick_comefrom, and
ick_nextfrom) make it possible to jump from an
INTERCAL program to a C program. Because C
doesn’t allow jumping into the middle of a function, there
has to be some way to create a block of code which can be
jumped into. This is what these two macros achieve.
This declaration and definition:
ICK_EC_FUNC_START(identifier)
{
/* code goes here */
}
ICK_EC_FUNC_END
is equivalent to this:
void identifier(void)
{
/* code goes here */
}
except that it is possible to jump from an
INTERCAL program into the declared and defined
program. (If you need to write a prototype for the function early,
void identifier(void); is perfectly acceptable, but an
early prototype is not required unless you call the function from
earlier within the C code.) Of course, you can substitute any
identifier that’s legal as a function name for
identifier (as long as it doesn’t start with
ick_ or ICK_). The resulting function is
a function (for instance, you can take its address or call it in
the usual ways); the only differences are that it can be jumped
into from INTERCAL code and that it is
constrained to take no arguments and return no data. (It can still
access global and INTERCAL variables.) If the
function is jumped into from INTERCAL code, but
then control flow reaches the end of the function, or the function
return;s but was not called from C, the resulting
behaviour is undefined; C-INTERCAL will attempt to
continue by some means at that point, but may fail. If a function
is unsure whether it gained control from C or from INTERCAL code,
it may use ick_return_or_resume (described below).
Because you are not allowed to declare two C functions with the
same name (even in different modules), all functions declared with
ICK_EC_FUNC_START must have unique names across the
entire compilation.
It is sometimes necessary for a C program to do its own initialisation
before the INTERCAL program starts running. To do so, it can use the
ick_startup macro inside a function declared with
ICK_EC_FUNC_START; the syntax is
ick_startup(block), where the argument is an expression,
statement, or compound statement to run. The argument itself must not
contain any ick_-prefixed macros or functions except possibly
ick_create, may have side effects, and must fit the C
preprocessor’s idea of what a macro argument should look like
(it’s more used to parsing expressions than blocks; the general
rule is to avoid commas except when they’re directly or
indirectly inside parentheses or strings).
A line label is something that can be NEXTed to and
COME FROM. Unlike an INTERCAL line
label, it does not label a statement, and therefore attempts to
ABSTAIN or REINSTATE it may be errors, or may
be ignored (it’s unspecified which, which means that either may
happen for any or no reason, but exactly one will happen in any given
case, although the choice might not be consistent).
The macro ick_linelabel(expression); may appear anywhere a
compound statement would normally be able to appear. (That is, it looks
like a function call being used as a standalone expression, but in fact
the places where it can appear are more limited.) In contrast to
ordinary line labels, an expression can be used rather than just a
constant; however, the behaviour is undefined if the expression has
side-effects. Upon encountering the line label, any COME
FROMs or NEXT FROMs aiming at the line label
(including ick_comefroms and ick_nextfroms)
will steal control from the program; RESUMING after a
NEXT FROM will work, but suffers from the same caveats as
setjmp/longjmp do (any auto variables that change their value between
the NEXT FROM and RESUME will have their
value clobbered (i.e. their value is no longer reliable and should not
be accessed)). Note that the INTERCAL variables are
immune to this problem. You can also avoid the problem by marking
variables as volatile in the C program.
It is possible to NEXT or ick_next to a
ick_linelabel, which has the same effect as saving the
NEXT stack, calling the function containing the
ick_linelabel and then immediately doing a C
goto to an imaginary label preceding it. Due to this
possibility, an ick_linelabel is only allowed within a
function defined with ICK_EC_FUNC_START.
In INTERCAL programs, labels don’t stand on
their own, but instead label a statement. The difference between a
standalone line label and a line label that labels a statement is that
COME FROMs will come from the label itself (which
is before the next statement) when aiming at a standalone line label,
but the end of the statement when aiming at a labeled
statement. To achieve the same effect in C, the macro
ick_labeledblock is available; it can be used as
ick_labeledblock(expression,expression) or
ick_labeledblock(expression,statement); the first argument
is the label, and the second argument is an expression or statement to
label (if an expression is labeled, it will be converted to a statement
that evaluates it for its side effects and discards the result). It is
even permitted to label a block statement in this way. Note, however,
that you have to contend with the C preprocessor’s ideas of where
macro arguments begin and end when doing this. Other than the position
of the COME FROM target created by the label, this behaves
the same way as ick_linelabel (so for instance, computed
line labels are allowed, but the expression that computes them must not
have side effects, and it is only allowed within a function defined
with ICK_EC_FUNC_START).
The ick_comefrom and ick_nextfrom macros are,
like the other INTERCAL flow control macros (as
opposed to functions), only allowed within a function defined with
ICK_EC_FUNC_START. They act almost exactly like the
INTERCAL statements of the same name (although note
that C statements cannot be ABSTAINed FROM
even if they act the same way as INTERCAL
statements); they are written as ick_comefrom(expression);
and ick_nextfrom(expression); respectively (note that they
must be called as statements, and cannot be used as part of an
expression). Whenever a standalone line label is encountered whose
expression evaluates to the same number as the expression inside the
ick_comefrom or ick_nextfrom, and that number
is at most 65535, then control will be transferred to the
ick_comefrom or ick_nextfrom, leaving a
NEXT stack entry behind in the case of
ick_nextfrom; likewise, if the end of a labeled statement,
expression or block is reached and the label has the right number. Some
caveats: the expression need not be constant, but must not have side
effects, must not be negative, and must fit into the range of an
unsigned long in the C program (and the statement will do
nothing if the expression evaluates to a value larger than 65535). In
keeping with the best C traditions, these caveats are not checked, but
instead result in undefined behaviour if breached.
There are also versions ick_comefromif and
ick_nextfromif, which take a second parameter, which is a
condition that specifies whether control is actually stolen from the
target. The condition may have side effects, and is only run when the
line numbers match; it should return 0 or NULL to leave control flow
alone, or nonzero to steal control, and should be either an integral
type or a pointer type. Although side effects are allowed, the
condition must not look at or alter auto or
register variables in the enclosing function, not even if
they are also marked volatile. (Global and
static variables are fine, though.)
ick_next is a macro that acts like the
INTERCAL statement NEXT. Contrary to
the other INTERCAL-like macros, it can be used in
any function regardless of whether it was defined with
ICK_EC_FUNC_START; however, it must still be used as a
statement by itself, and a call to it looks like
ick_next(expression);. The expression is the label to
NEXT to, and works under the same rules as the expressions
for ick_comefrom; it need not be constant (unlike in
C-INTERCAL!), but must not have side effects, must not be
negative, must fit into the range of an unsigned long, and is ignored
if it is over 65535. If there happen to be multiple labels with the
correct value at the time, the compiler will NEXT to one
of them. Bear in mind that there is a limit of 80 entries to the
NEXT stack, and that this limit is enforced.
If the resulting NEXT stack entry is RESUMEd
to, the program will continue after the ick_next as if via
setjmp, with all the usual restrictions that that entails;
if the resulting NEXT stack entry is forgotten, then the
ick_next call will never return. (Note that the ’as
if via setjmp’ condition allows you to preserve the vales of
auto and alloca-allocated storage as long as
its value has not changed since the ick_next was called,
which is a significantly more lenient condition than that normally
imposed on such variables (see External Calls and auto).)
ick_resume is a macro, but there are few restrictions on
its use; it is permitted to use it inside an expression (but it returns
void, making this not particularly useful), and acts like a function
which takes an unsigned short argument, returns void, and has a
prototype (but you cannot take its address; if you need to be able to
do that, write a wrapper function for it). It can be used within any
function regardless of how it was declared, and never returns; instead,
it pops the specified number of NEXT stack entries and
resumes execution at the last one popped, just as the
INTERCAL statement does. This causes the same errors
as the INTERCAL statement if the number of entries
popped is zero or larger than the NEXT stack.
There is also a macro ick_return_or_resume();; it can only
be used inside a function defined with ICK_EC_FUNC_START,
and is equivalent to return; if the function was called
from C, or ick_resume(1); if the function was called from
INTERCAL. It’s therefore a safe way to return
from such a C function if you don’t know how control reached it
in the first place.
The ick_forget macro removes NEXT stack
entries, and the corresponding C stack entries. It must be called as a
statement by itself, and its invocation looks like this:
ick_forget(expr);, where the expression is the number of
NEXT stack entries to forget (all of them will be
forgotten if the number is higher than the number of entries). The
expression will be casted to an unsigned short.
ick_forget can only be used inside a function declared
with ICK_EC_FUNC_START. As it is removing stack entries
both in INTERCAL and in C, it will clobber the value
of all auto variables created since the highest remaining
NEXT stack entry came into being (or since the start of
the program, if the NEXT stack is emptied by the command)
and also deallocate all alloca storage allocated since
then. It also causes the return address of the current function to
become undefined, so that function must not return; control may leave
it via RESUME, or via COME FROM, or via
NEXT or NEXT FROM followed by the relevant
NEXT stack entry being forgotten (the function is still
’running’ but suspended while the NEXT stack
entry still exists). (Note that these restrictions are stronger than
those on RESUME; this is because RESUME
preserves most of the stack, but FORGET destroys parts of
the stack and therefore cannot avoid destroying the data stored there.
It could be much worse; a previous (never released) version of the code
didn’t remove those parts of the stack in many circumstances,
leading to a stack leak that caused programs to segfault after a
while.)
This class of four functions make it possible to get and set INTERCAL scalar variables from C code. Their prototypes are as follows:
uint16_t ick_getonespot(unsigned short varnumber); void ick_setonespot(unsigned short varnumber, uint16_t newvalue); uint32_t ick_gettwospot(unsigned short varnumber); void ick_settwospot(unsigned short varnumber, uint32_t newvalue);
The program will error out with a fatal error (see E200) if the variable you request is mentioned nowhere in
the INTERCAL program; if you attempt to set an
IGNOREd variable, the attempt will silently fail (just as
if you assigned to it in an INTERCAL program). The
get functions are safe to use in a computed line label, so you can use
them to produce computed line labels that depend on
INTERCAL variables. (uint16_t and
uint32_t are standard C data types; if your system
doesn’t provide them, get better system header files.)
If you care about speed, note that .1 is the fastest variable of all to access, and otherwise variables first mentioned near the top of the INTERCAL program will be faster to access than variables mentioned lower down.
The ick_create function (prototype: void
ick_create(char*, unsigned long)) allows the external calls
system to be used to create new INTERCAL syntax; to
do this, you give a ‘signature’ representing the syntax you
want to define and a line number to the function (which are its two
arguments, respectively). The signature defines the syntax that you are
defining; whenever that syntax is encountered within the
INTERCAL program, it will NEXT to the
line number you specify, which can do various clever things and then
RESUME back to the INTERCAL program (or
if you’re defining a flow-control operation, you might want to
leave the NEXT stack entry there and do other things).
However, note that the overloading of :1601, etc., will
still take place as in the INTERCAL version of
CREATE if the -a option is used (see -a), so care is needed when writing flow control
statements that they work both with and without the option and
don’t cause STASH leaks (which means no
FORGETting the relevant NEXT stack entry, and
no looking at 1600-range variables). This allows the external calls
system to define whole new INTERCAL commands, with
the same power as any other programming language.
There are various restrictions on what syntax you can
CREATE with this method, which are best explained by an
explanation of the relevant C-INTERCAL compiler internals.
When an INTERCAL program is compiled by
C-INTERCAL, any unrecognised statements it comes across
are compiled by a ‘just-in-case’ compiler that attempts to
compile them anyway with no knowledge of their syntax, just in case the
syntax becomes defined later. (E000 (see E000) will
be thrown when such statements are encountered at runtime, unless the
syntax has been CREATEd since to give a statement a
meaning.) For the just-in-case compiler to run, the resulting statement
must be completely unrecognised; this means that it may contain no
keywords (not even a sequence of letters that forms a keyword, such as
FROM or DO), it must consist only of variable
names, expressions, and capital letters other than
‘V’ (because ‘V’ is a
unary operator, so otherwise there would be ambiguity), and in which
any two variable names or expressions are separated by at least one
capital letter. The compiler will produce a ‘signature’ for
the unknown command that can be defined.
A signature consists of a sequence of characters (and is represented as
a null-terminated string; the runtime makes a shallow copy of the
string and keeps it until the end of the program, so arrangements must
be made to ensure that the storage in which the string is allocated
stays around that long, but this opens up interesting possibilities in
which the signature that was actually CREATEd can be
modified retroactively); whitespace is not allowed in a signature.
Capital letters can be used (apart from ‘V’),
and match the same capital letters literally in the
INTERCAL syntax being created; also available are
the special characters ‘.,;~’, which match
respectively a scalar variable (a onespot or twospot variable such as
:1), an array variable (such as ;2), an array
element (such as ,3 SUB #4 #5), and an expression that
isn’t a variable name and isn’t an array element (such as
.4$.5). If you want to be able to match other things (say,
to be able to match all expressions), you will need to submit multiple
signatures using multiple calls to ick_create; maybe you
could write a library to do that automatically.
CREATEd operators also have signatures, but of quite a
different form. The signature for a single-character operator is a
lowercase u, followed by its character code in hexadecimal (no leading
zeros, and in lowercase); the signature for an overstrike is a
lowercase o, followed by the lower relevant character code in
hexadecimal, followed by a lowercase x, followed by the higher relevant
character code in hexadecimal.
The routine that is NEXTed to will presumably want to be
able to see what in the INTERCAL program was matched
by the signature, so a range of function-like macros is provided to
access that. They must be run from within the invocation of the
function which was NEXTed into by the created syntax (see
External Calls and auto for when
a function invocation ends, which could be sooner than you think when
the C-INTERCAL external calls system is used), and are
undefined behaviour when that invocation did not gain control from a
CREATEd statement. Here are their effective prototypes:
int ick_c_width(int); int ick_c_isarray(int); unsigned short ick_c_varnumber(int); uint32_t ick_c_value(int); /* These require -a to work */ uint32_t ick_c_getvalue(int); void ick_c_setvalue(int, uint32_t);
The first argument to all these macros is the position of the match in the signature (0 for the first non-capital-letter match in the signature, 1 for the second, and so on until no more items are left in the signature to match); specifying a position that isn’t in the signature is undefined behaviour.
ick_c_width returns the data type, as a width in bits, of
the expression (or the width in bits of an element of the passed in
array), and ick_c_isarray returns 1 if the argument was an
array variable or 0 if it was an expression (array elements and scalar
variables are expressions). ick_c_varnumber returns the
variable’s number (for instance 123 for .123), or 0
if the corresponding argument was not a variable; in the cases where
the argument was a variable, these three functions together provide
enough information to figure out which variable (which is useful if
you’re writing an extension which takes a variable name as an
argument).
ick_c_value returns the value of the corresponding
expression at the time the CREATEd command was called;
ick_c_getvalue is almost equivalent, but only works if the
-a option (see -a) was used
during compilation, and returns the value of the corresponding
expression now. (The uint32_t return type is large enough to hold
either a onespot or twospot value, and will be zero-extended if the
corresponding expression had onespot type.) ick_c_setvalue
also depends on -a, and will assign to the corresponding
expression (be careful not to provide a value that is too large for
it!). In the case that the corresponding expression is not a variable,
this will attempt to perform a reverse assignment to the expression,
and can produce ordinary INTERCAL errors if it
fails. It is not possible to redimension an array this way, as this is
assignment, not a calculate operation.
Because the external calls system merges the
INTERCAL NEXT stack with the C return
value and data storage stack (note for pedants: the C standards nowhere
mandate the existence of such a stack, or even mention one, but the
restrictions stated in them imply that implementations have to act as
if such a stack existed, because of the way the scoping rules and
recursion work), the external calls system therefore has severe effects
on data that happens to be stored there. (In
INTERCAL terms, imagine what would happen if data
could be stored on the NEXT stack; if C used the more
sensible system of having a STASH for each variable, these
problems would never occur in the first place, instead causing an
entirely different set of problems.) Similar considerations apply to
the common nonstandard C extension alloca, which
dynamically alters the size of the stack; also, in what goes below,
register variables should be considered to be
auto, because the compiler may choose to allocate them on
the stack. Theoretical considerations would lead one to conclude that
variable-length arrays should obey most of the same restrictions; in
practice, though, it’s unwise to attempt to mix those with
INTERCAL code at all, except by separating them into
separate functions which aren’t flagged with
ICK_EC_FUNC_START and use no ick_-prefixed
identifiers, even indirectly. (They may cause a compile to fail
completely because they don’t mix well with goto.)
In the description below, INTERCAL commands should be taken to include the equivalent C macros.
NEXT/NEXT FROM paired with
RESUME have the least effect, and the most obvious effect,
on auto variables in the function that was
NEXTed from, which is the same effect that the standard C
function longjmp has. That is, alloca storage
stays intact, and auto variables have their values
‘clobbered’ (that is, their value is no longer reliable and
should not be used) if they changed since the corresponding
NEXT and are not marked as volatile. (This is
a very easy restriction to get around, because changing the values of
such variables is quite difficult without using statically-allocated
pointers to point to them (a dubious practice in any case), and
volatile is trivial to add to the declaration.)
COME FROM has more restrictions; it deallocates all
alloca storage in the function that was COME
FROM, and functions that called it or that called functions that
called it, etc., using C calls (as opposed to NEXT), and
those invocations of the functions will cease to exist (thus destroying
any auto variables in them), even in the case of
COMING FROM a function into the same function.
auto variables in the function that is come into will
start uninitialised, even if initialisers are given in their
declaration, and it will be a ‘new’ invocation of that
function. (It is quite possible that the uninitialised values in the
auto variables will happen by chance to have the values
they had in some previous invocation of the function, though, because
they are likely to be stored in much the same region of memory; but it
is highly unwise to rely on this.) Note that volatile will
not help here. Observant or source-code-reading readers may note that
there is a mention of an ick_goto in the source code to
C-INTERCAL; this is undocumented and this manual does not
officially claim that such a macro exists (after all, if it did, what
in INTERCAL could it possibly correspond to?), but
if such a macro does exist it obeys the same restrictions as COME
FROM.
FORGET is the worst of all in terms of preserving data on
the stack; it deallocates alloca data and clobbers or
deletes auto variables in all function invocations that
have come into existence since the NEXT that created the
topmost remaining NEXT stack entry was called, or since
the start of the program if the NEXT stack is emptied, and
the current function will continue in a new invocation.
volatile is useless in preventing this, because the
relevant parts of the stack where the data were stored are deleted by
the command (that’s what FORGET does, remove stack).
If any of these data are required, they have to be backed up into
static storage (variables declared with static or global
variables), or into heap storage (as in with malloc), or
other types of storage (such as temporary files) which are not on the
stack. (Incidentally, suddenly deleting parts of the stack is excellent
at confusing C debuggers; but even RESUME and COME
FROM tend to be sufficient to confuse such debuggers. More
worrying is probably the fact that the C standard provides a portable
method for deleting the stack like that, and in fact the external calls
runtime library is written in standard freestanding-legal C89 (with the
exception of +printflow debug output which requires a
hosted implementation), meaning that in theory it would be possible to
split it out to create an implementation of a C-plus-COME-FROM-and-NEXT
language, and doing so would not be particularly difficult.)
Note that INTERCAL variables are not stored on the C stack, nor are any of the metadata surrounding them, and so are not affected unduly by control flow operations.
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| no | version 0.29+ | no | no |
C-INTERCAL supports linking INTERCAL programs with Funge-98 programs (to be precise, only Befunge-98 programs are currently supported). However, it does not ship with a Funge-98 interpreter, and such an interpreter needs to be linked to the resulting program in order to run the Befunge program. Therefore, you need to convert a third-party Funge-98 interpreter to a library usable by C-INTERCAL before you can use this part of the external calls system (see Creating the Funge-98 Library); however, this only has to be done once.
Once the library has been created, you can link an
INTERCAL program with a Befunge-98 program by
invoking ick like this:
ick -e intercalprogram.i befungeprogram.b98
You can link no more than one Befunge-98 program at once (just like you can link no more than one INTERCAL program at once). Also, the INTERCAL program must come first on the command line.
It is legal to link INTERCAL, C, and Befunge-98 simultaneously; however, the identifiers used in the third-party Funge-98 interpreter have not been mangled to avoid collisions, and therefore problems may be caused if the C program uses the same identifiers as the Funge-98 interpreter.
Before external calls to Funge-98 can be used, the relevant library must be compiled. (After the library has been compiled, then you will need to reinstall C-INTERCAL; however, you will not need to recompile C-INTERCAL.)
At present, only the cfunge Funge-98 interpreter (https://launchpad.net/cfunge/+index) can be converted into a library suitable for use by C-INTERCAL; also, doing this is only supported on POSIX systems (although if someone gets it to work on DOS/Windows, the author of this manual would be interested to hear about it). Also, a source-code distribution (rather than a binary distribution) is needed. One way to obtain the latest cfunge sources is via the bzr version-control system, using the following command (correct as of the time of writing, but as always, links can become dead):
bzr branch lp:cfunge
(As a licensing note, note that cfunge is licensed under the GNU General Public licence version 3, whereas C-INTERCAL is licensed under version 2 and all later versions of that licence; although these terms are obviously compatible with each other, you must ensure yourself that your program has appropriate licensing terms to allow a GPLv3 library to be linked to it.)
Once you have downloaded the cfunge sources, you need to compile them
into a library suitable for use with C-INTERCAL (note that
this is a somewhat different process to compiling them into a
standalone Funge-98 interpreter). There is a script provided in the
C-INTERCAL distribution to do this,
etc/cftoec.sh. It must be run in the etc
subdirectory of the C-INTERCAL distribution (i.e. the
directory the script itself is in), and must be given the path to the
root directory of the cfunge source distribution (that is, the
directory that contains the src, lib and
tools subdirectories of that distribution) as its only
argument. Note that it may give some compiler warnings on compilation;
my experience is that warnings about C99 inlining can be safely ignored
(they reflect a deficiency in gcc itself that luckily
seems to be irrelevant in this case), but other warnings may indicate
problems in the exact versions of the sources that you downloaded (and
errors definitely indicate such problems).
Once the library has been created, it will appear as the new file lib/libick_ecto_b98.a in the C-INTERCAL distribution (the cfunge distribution will be left unchanged); reinstalling C-INTERCAL will install this file to its proper location. (It is also in a valid location to be able to be run if you aren’t installing C-INTERCAL but instead just running it from the distribution’s directory.)
This section will not make much sense to a non-Funge programmer; therefore, if you are not used to Funge, you probably want to skip it.
To a Funge program, the external calls interface is accessed via a Funge-98 ’fingerprint’ defined by the interpreter. The name of the fingerprint is 0x49464649, or as text, ‘IFFI’.
When a program formed by linking INTERCAL and Befunge-98 is run, the first thing that happens is some internal INTERCAL initialisation which is not visible to either program, and then initialisation routines specified in the Befunge-98 program run (if an initialisation routine is also specified in a linked C program using ick_startup, it is unspecified whether the C or Befunge-98 initialisation happens first.) In the Befunge program, the initialisation routine consists of everything that happens until the ‘Y’ command in the ‘IFFI’ fingerprint is run; the author of the Funge-98 must load the ‘IFFI’ fingerprint themselves during this initialisation to access that command. (This is so that the Befunge program ends up complying with the Funge-98 standard; commands not defined in that standard cannot be used until a fingerprint is loaded.) During initialisation, no commands from the ‘IFFI’ fingerprint may be used except ‘Y’ and ‘A’. (If a different command is used, ‘C’, ‘M’, and ‘X’ remove the arguments they would use from the stack (if any) but otherwise do nothing, and the other commands in the ‘IFFI’ fingerprint reflect.)
After the ‘Y’ command is called, the
INTERCAL program starts running; in order for the
Befunge program to regain control, it has to be NEXTed to
from the INTERCAL program, or COME or
NEXT FROM the INTERCAL program, or
contain the line label to which syntax in the
INTERCAL program was CREATEd. (In other
words, the normal INTERCAL ways of transferring
information between parts of a program.) In order to do this,
therefore, line labels and INTERCAL control flow
statements must be placed into the Befunge program.
Code like COME FROM (100) is a single statement in
INTERCAL, but several statements in Funge-98;
therefore, some method of telling the interpreter where to start
executing to look for COME FROMs, NEXT FROMs,
and line labels is needed. The method used by C-INTERCAL
is that of the ’marker’; a marker is represented by
character 0xB7 (a mid-dot in Latin-1) in the input Funge-98 program,
but is transformed to a capital ‘M’ by
ick. (The reason for using a special character for a
marker and transforming it rather than just using
‘M’ is to prevent occurences of
‘M’ in comments and string literals, etc.,
having an effect on the control flow of the program.) Whenever a
NEXT or line label is encountered (in the
INTERCAL program, the Funge program or elsewhere),
the Funge program is executed starting from each marker in each
cardinal direction to look for line labels or
COME/NEXT FROMs respectively. Therefore,
COME FROM (100) is written in Funge-98 as
Maa*C (where the M is a marker in the source code), and
likewise the line label (100) would be written as
Maa*L. (This code can be written in any cardinal
direction, that is left to right, top to bottom, right to left, or
bottom to top, but not diagonally or flying.) There are likely to be
unused directions from markers, which will be evaluated too; you can
(and must) close these off by reflecting code execution back into that
marker, another marker, or a non-marker M. Note also that
a marker remains in Funge-space even if the M on the same
square is deleted (the marker itself is not visible to the
g command, though).
Here are the commands in the ‘IFFI’ fingerprint:
A
This command pops a line number and then an 0"gnirts"-format string
from the stack; they are used as the line number and signature to
CREATE syntax in the INTERCAL
program; for details of the format of the signature, see ick_create. Although using this command
during speculative execution works, doing so is not recommended; if
the target line number for CREATEd syntax is changed
during speculative execution to find the line that that syntax
corresponds to, its effect is delayed until after the original line
is found and execution continues from that point. (Side effects
during speculative execution are never recommended, because they
might or might not be optimised away.)
C
During speculative execution to find COME FROMs and
NEXT FROMs, pops a line label off the top of the stack
and does a COME FROM that location. During speculative
excution to find line labels, pops the top of the stack and ends
that particular speculative execution as a failure. When not doing
speculative execution, pops and discards the top element of the
stack.
D
This command must only be used when the Funge program is executing
a CREATEd command, and allows access to the arguments
that command has. It pops an integer off the top of the stack, and
treats it as an argument position (0-based, so 0 refers to the
first argument, 1 refers to the second, and so on). Note that
providing an invalid argument number, or running this command when
not implementing a CREATEd command, leads to undefined
behaviour (possibly a reflection, possibly a segfault, possibly
worse).
The command pushes information about the argument chosen onto the stack; the following information is pushed from bottom to top:
.123 would push 123 here, but
.1~.2 would push 0).
CREATEd instruction was called.
F
During speculative execution, this command reflects; otherwise,
this command pops an integer from the top of stack, and
FORGETs that many NEXT stack entries (or
all of them if the argument given is negative).
G
This command pops an integer from the top of stack. If it is positive, the value of the onespot variable whose name is the popped integer is pushed onto the stack; if it is negative, the value of the twospot variable whose name is minus the popped integer is pushed onto the stack; and if it is zero, the command reflects. If the referenced variable is not in the INTERCAL program at all, this causes an INTERCAL error due to referencing a nonexistent variable.
L
During speculative execution to find COME FROMs and
NEXT FROMs, this command pops and discards the top
stack element, then ends that speculative execution. During
speculative execution to find a line label, this command pops an
integer from the top of stack and succeeds with that integer as the
line label (that is, it is possible to NEXT to an
L in the Funge program if a marker, followed by code
to push the correct line number onto the stack, precedes that
L). When not doing speculative execution, the integer
on the top of the stack is used as a line label (assuming it is in
the range 1–65535, otherwise it is popped and discarded), and
a search is made for COME FROMs and NEXT
FROMs aiming for that line label (including in the
INTERCAL program and the Befunge program itself,
as well as programs in any other language which may be linked in).
Note that just as in INTERCAL, it is possible to
NEXT to a line label which has a COME
FROM aiming for it, in which case the COME FROM
will come from that line label as soon as the NEXT
transfers control to it.
M
Does nothing if not in speculative execution, or ends the current speculative execution with failure. (This is so that code like
v >M5C ^
does exactly the same thing as COME FROM (5), even
when, for instance, it is entered from the left in the Funge
program, rather than gaining control from the line label
(5).)
N
During speculative execution, reflects. Otherwise, pops the top
stack element, interprets it as a line label, and
NEXTs to that line label (this may start speculative
execution to look for line labels, but might not if it isn’t
needed, for instance if the line label in question is in the
INTERCAL program or in a C program linked to the
Befunge program).
R
During speculative execution, reflects. Otherwise, pops the top
stack element, removes that many items from the NEXT
stack, and RESUMEs at the last item removed. (If the
top stack element was zero, negative, or too large, this will cause
a fatal error in the INTERCAL program.)
S
Pops a variable number (interpreted as onespot if positive, or minus the number of a twospot variable if negative) and an integer from the stack, and sets the referenced variable to the integer. This reflects if an attempt is made to set the nonexistent variable 0, causes a fatal error in the INTERCAL program if an attempt is made to set a variable that doesn’t exist there, and does not set read-only variables (but pops the stack anyway). If the integer is too high for the variable it is being stored in, only the least significant 16 or 32 bits from it will be used; and likewise, if it is negative, it will be treated as the two’s complement of the number given.
V
Pops a CREATEd argument index and an integer from the
top of stack. (This is undefined behaviour if not in the
implementation of a CREATEd statement, or if the
referenced argument does not exist; as with the D
instruction, 0 refers to the first argument, 1 to the second, and
so on.) If the -a option is not used, this command
does nothing; otherwise, the value of the argument will be set to
the integer. (This involves doing a reverse assignment if the
argument is a non-variable expression, as usual, and causes a fatal
error in the INTERCAL program if the reverse
assignment is impossible or an attempt is made to assign a scalar
to an array.)
X
This is identical to C, except that it does a
NEXT FROM rather than a COME FROM.
As with external calls to C, terminating any program involved (whether
the INTERCAL program with GIVE UP, the
Befunge program with @ or q, or a C program
with exit()) causes all programs involved to terminate,
and likewise a fatal error will end all programs with an error.
One final point which is probably worth mentioning is that flow control
instructions only record the IP’s position and direction, nothing
else; so for instance, if the stack is modified in one part of the
code, those modifications will remain even after a RESUME,
for instance.
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| no | version 0.29+ | no | no |
It is possible to specify other information to the external calls system by using the filename list after all the options are given. To be precise, certain filename patterns are recognised and used to change the options that are used to compile the externally-called files.
The ‘.c99’ extension is treated identically to
‘.c’, except that it causes the file with that
extension to be preprocessed as C99 (the more modern version of the C
standard, the older C89 is more common), and that all C files involved
will be compiled and linked as C99. (This corresponds to
-std=c99 in gcc.) Likewise, the
‘.c11’ extension can be used to indicate C11.
The ‘.a’ extension indicates that an
object-code library should be linked in to the final program. This is
most commonly used to link in the maths library libm.a and
other such system libraries. If the filename is of the form
‘lib*.a’, then the file will be searched for
in the standard directories for libraries on your system, and also
where the C-INTERCAL libraries are stored (which may be
the same place); otherwise, the current directory will be searched.
(Specifying libm.a on the command line corresponds to
passing -lm to gcc.)
Whatever language your source files are written in, when -e is used (see -e), the compiler will go through much the same steps.
First, the INTERCAL program specified is compiled
into a C program that uses the INTERCAL external
call conventions for its control flow operations. The resulting
‘.c’ file will be left behind in the same
directory (even if -g isn’t used); if you look at
it, you’ll see the #include <ick_ec.h> line,
and the other hallmarks of an external call program (for instance,
INTERCAL NEXTs will translate into
slightly modified ick_nexts; the modification is simply to
allow the correct line number to be displayed in case of error).
After that, the resulting files are preprocessed twice. First, the C
preprocessor is run on the files; then, a special
C-INTERCAL ‘preprocessor’ is run on the files.
(‘Preprocessor’ is a bit of a misnomer here, as it’s
near the end of the compilation process; ‘postprocessor’
would likely be more accurate, or maybe ‘interprocessor’.)
Its job is to fix line labels between the gotos that are used to
implement jumping into the middle of a C function, to assign unique
numbers to things that need them, and to keep track of which functions
need to be checked for line labels and for COME FROMs and
NEXT FROMs. The resulting file will have the extension
‘.cio’; it is almost human-readable,
especially if you run it through a C code indenter, and consists of C
code (which might be a thin wrapper around some other language) and
instructions to gcc. The ‘.cio’
file will be left behind for you to look at, if you like.
Once the ‘.cio’ files have been produced,
gcc is used to compile all the
‘.cio’ files and link them together into an
executable; the executable will have the same name as the
INTERCAL source, minus any extension (and on DJGPP,
assuming that its version of gcc could handle the
resulting command line (not necessarily guaranteed), a
‘.exe’ extension is added), and will consist
of all the C files linked together with the
INTERCAL. Any functions named main in
the C files will be deleted; likewise, if there is a name clash between
any two functions, the one in the file named earlier on the command
line will be used. There is presumably some use for this feature,
although I haven’t figured out what it is yet.
Extending this to other compiled languages is mostly a problem of
determining how they fit into the INTERCAL control
structure, which is not a trivial task, and of figuring out how to link
them to C code, which in some cases is trivial (especially if the
language is one that gcc can compile!) and in other cases
is very difficult. If anyone has any ideas of new languages that could
be added to the external calls system, feel free to contact the current
C-INTERCAL maintainer with suggestions or patches.
| INTERCAL-72 | C-INTERCAL | CLC-INTERCAL | J-INTERCAL |
|---|---|---|---|
| no | version 0.28+ | no | no |
The C-INTERCAL distribution comes with libraries that can
be used to extend its capabilities; they are implemented using the
external call mechanism, and are in effect standard files to include
using that mechanism. To use an expansion library, give the
-e option to ick (note that this means you
cannot use them with the debugger or profiler, nor with multithreaded
or backtracking programs), and specify the expansion library’s
name at the end of the command line (or to be precise, anywhere after
the initial INTERCAL file). The libraries themselves
are written in C and have a ‘.c’ extension,
and are human-readable; C-INTERCAL will look for them in
the same places as it looks for the system library (including in the
current directory, so you can test your own expansion libraries without
having to install them).
Expansion libraries use C identifiers which start with the string ‘ick_my_’ (this is not used by the compiler, and is explicitly not affected by the prohibition on identifiers starting ‘ick_’ when writing an expansion library), and use line labels in the range (1600) to (1699). (Most programs will be avoiding this range anyway, because it’s inside the (1000) to (1999) range reserved for the system library, but the system library doesn’t use it, in much the same way that the identifiers used are inside the range reserved for the compiler, but the compiler doesn’t use them.)
Expansion libraries are available from C-INTERCAL version 0.28; CLC-INTERCAL has a similar concept (that of ‘preloads’), but implemented a completely different way.
syslibc is an implementation of the base-2 INTERCAL system library in C (see System Libraries); using it in programs running in other bases is accepted by the compiler, but likely to produce unpredictable results. When using this expansion library, you also need to give the -E option (see -E) so that the main system library is not included, or it will be used in preference to the expansion library. All documented features of the INTERCAL base-2 system library are implemented, but most undocumented features are not, so INTERCAL programs which relied on them (dubious behaviour in any case) will not work with syslibc. The main reason to use this library is to increase the speed of an INTERCAL program; however, note that the speed gains in arithmetic will be accompanied by the performance penalty of using the external calls infrastructure, unless you were already using it.
As an example of using ick_create, a very simple expansion
library is provided to enable a computed NEXT capability, by defining a
new command COMPUNEX. It is used as DO .1
COMPUNEX (allowing any expression in place of the .1), and is
similar to an ordinary NEXT, but has two limitations: it
takes up two NEXT stack entries, and the top one should
not be RESUMEd past or forgotten (thus it isn’t a
particularly useful command, except maybe to produce the equivalent of
something like function pointers). By the way, note that
C-INTERCAL avoids computed NEXT mainstream
for much the same way that CLC-INTERCAL avoids
NEXT altogether; it makes things too easy. This example is
provided mostly just to demonstrate the syntax, and the care that needs
to be taken with implementing flow control operators.
‘compunex’ is double-deprecated; an
alternative is the following sequence of commands involving computed
CREATE:
DO CREATE .1 ABC DO ABC
This sequence emulates all features of NEXT (although it
has different gerunds and is two statements, not one), making it much
more useful for simulating computed NEXT than
COMPUNEX is. (There’s no need to avoid forgetting
the return value; although this skips the CREATE cleanup,
none is required because the created statement ABC (any
other statement would do just as well) takes no arguments.)
The C-INTERCAL compiler exists in a world of several other compilers.
The Princeton compiler was the first INTERCAL
compiler available, and compiled INTERCAL-72. Using
convickt (see convickt) to
translate its programs from the original EBCDIC to Latin-1 or
Atari-syntax ASCII is required to run them under the
C-INTERCAL compiler, but apart from that there should be
no problems; everything that that compiler can do can be reproduced by
C-INTERCAL, even including some of its bugs. The only
potential problems may be where constructs were nonportable or dubious
to begin with (such as the IGNORE/RETRIEVE
interaction), or where commands intended to be syntax errors were used
in the program but have a meaning in C-INTERCAL. For extra
portability, it’s possible to use the -t compiler
option to ick (see -t) to tell it
to interpret the program as INTERCAL-72, but as
C-INTERCAL’s dialect of INTERCAL
is basically backward-compatible anyway this mostly serves to check
newer programs for compatibility with older compilers.
The Atari compiler was an uncompleted implementation of
INTERCAL-72, optimistically pre-described in some 1982
additions to the original INTERCAL-72 manual. Despite the
implementation’s never actually existing, the documentation of
the syntax provided a model for C-INTERCAL. If any Atari
800 INTERCAL source code actually existed, there would be no need to
use convickt on it.
The J-INTERCAL compiler is an implementation of
INTERCAL written in Java that compiles
INTERCAL into Java (and so has a similar
relationship with Java to that of the C-INTERCAL compiler
(which is written in C and compiles into C) with C).
J-INTERCAL has much the same feature set as older versions
of C-INTERCAL, with a few changes (such as the addition of
Esperanto and error messages coming up in different situations).
J-INTERCAL programs should run fine on
C-INTERCAL without trouble (as it is also an Atari syntax
compiler), except in nonportable cases such as
IGNORE/RETRIEVE interaction.
The CLC-INTERCAL compiler is the most modern INTERCAL compiler apart from C-INTERCAL (both compilers are maintained and updated every now and then as of the time of writing, so which is more modern is normally a matter of when you happen to check). Unlike the other three compilers mentioned above, it has a quite significant feature set, including many features not implemented or only partially implemented in C-INTERCAL, and is responsible for the origin of many of the features added in more recent versions of C-INTERCAL. Generally speaking, a CLC-INTERCAL program that uses its advanced features is unlikely to run on C-INTERCAL, or vice versa, whatever you do (apart from completely rewriting the more advanced parts of the program).
However, there are certain steps that can be taken to transfer less
advanced programs from one compiler to the other. First, translate the
program to Latin-1 Princeton syntax (if translating from
CLC-INTERCAL to C-INTERCAL) or Atari syntax
(if translating from C-INTERCAL to
CLC-INTERCAL), maybe using convickt, if
necessary. (Note that here the program is being translated to the
syntax that is not default for the target compiler.) Then use
command-line arguments to switch the compiler into the correct
emulation mode for the other compiler; C-INTERCAL uses the
options -xX, and on CLC-INTERCAL this is done
by selecting the appropriate preloads, or by changing the
program’s file extension to ‘.ci’. In
each case other options may be needed to turn on various extensions
(maybe -m or -v if translating to
C-INTERCAL, maybe the preload for gerund-based COME
FROM if translating to CLC-INTERCAL), and if
translating to CLC-INTERCAL you need to append the system
library to your program yourself because CLC-INTERCAL
doesn’t load it automatically.
In the case of very simple programs, or if you want to spend the effort
in translating compiler-specific code from one compiler to another, you
may be able to work without emulation options. (This is a good target
to aim for, in any case.) In such a case, you would do nothing other
than possibly edit the program to be more portable and a possible
character set and syntax change using convickt. If you
need compiler-specific code, you may be able to detect the compiler in
the code itself and adapt accordingly; making use of the
IGNORE/RETRIEVE interaction is one way to do
this, as it differs between C-INTERCAL,
J-INTERCAL, and CLC-INTERCAL. The other
things to watch out for when doing this are that
CLC-INTERCAL needs an explicit option to enable the use of
NEXT, that CLC-INTERCAL doesn’t load
the system library itself (you need to manually append it to the end of
the program) and that you probably shouldn’t number a line (666)
unless you know what you’re doing, because that line number has a
special meaning in CLC-INTERCAL.
The following table explains the equivalences between the various
character sets used for INTERCAL: 7-bit ASCII Atari
syntax, 5-bit Baudot Princeton syntax, 8-bit EBCDIC Princeton syntax,
and 8-bit Latin-1 Princeton syntax. (The Baudot and EBCDIC are the
CLC-INTERCAL versions, which are used by
INTERCAL compilers but basically nowhere else.) The
characters themselves are not shown in the table below, because they
would have to be shown in some syntax, which would be misleading.
(Atari syntax is used throughout this manual; you could convert from
that, assuming you have an ASCII table handy.) You can also use the
convickt command-line tool to translate
INTERCAL programs from one format to another (see
convickt). Note that Baudot has more than one
’shift state’; the shift state (1, 2, 3, or 4) is written
before the hexadecimal code for each character, and * represents a
character available in every shift state. To change from one shift
state to another, use character 1f to change from shift states 3 or 4
to 1, or from 1 or 2 to 2, and character 1b to change from shift states
1 or 2 to 3, or from 3 or 4 to 4.
| Atari | Baudot | EBCDIC | Latin-1 |
|---|---|---|---|
| 09 | N/A | 09 | 09 |
| 0a | * 02 | 0a | 0a |
| 0d | * 08 | 0d | 0d |
| 20 | * 04 | 40 | 20 |
| 21 | 3 0d | 4f | 21 |
| 22 | 3 11 | 7f | 22 |
| 23 | 4 06 | 7b | 23 |
| 24 | 4 01 | 4a | a2 |
| 25 | 4 1c | 6c | 25 |
| 26 | 3 1a | 50 | 26 |
| 27 | 3 0b | 7d | 27 |
| 28 | 3 0f | 4d | 28 |
| 29 | 3 12 | 5d | 29 |
| 2a | 4 09 | 5c | 2a |
| 2b | 4 03 | 4e | 2b |
| 2c | 3 0c | 6b | 2c |
| 2d | 3 03 | 60 | 2d |
| 2e | 3 1c | 4b | 2e |
| 2f | 3 1d | 61 | 2f |
| 30 | 3 16 | f0 | 30 |
| 31 | 3 17 | f1 | 31 |
| 32 | 3 13 | f2 | 32 |
| 33 | 3 01 | f3 | 33 |
| 34 | 3 0a | f4 | 34 |
| 35 | 3 10 | f5 | 35 |
| 36 | 3 15 | f6 | 36 |
| 37 | 3 07 | f7 | 37 |
| 38 | 3 06 | f8 | 38 |
| 39 | 3 18 | f9 | 39 |
| 3a | 3 0e | 7a | 3a |
| 3b | 3 1e | 5e | 3b |
| 3c | 4 0f | 4c | 3c |
| 3d | 4 07 | 7e | 3d |
| 3e | 4 12 | 6e | 3e |
| 3f | 4 0c | 65 | a5 |
| 40 | 3 19 | 6f | 3f |
| 41 | 1 03 | c1 | 41 |
| 42 | 1 19 | c2 | 42 |
| 43 | 1 0e | c3 | 43 |
| 44 | 1 09 | c4 | 44 |
| 45 | 1 01 | c5 | 45 |
| 46 | 1 0d | c6 | 46 |
| 47 | 1 1a | c7 | 47 |
| 48 | 1 14 | c8 | 48 |
| 49 | 1 06 | c9 | 49 |
| 4a | 1 0b | d1 | 4a |
| 4b | 1 0f | d2 | 4b |
| 4c | 1 13 | d3 | 4c |
| 4d | 1 1c | d4 | 4d |
| 4e | 1 0c | d5 | 4e |
| 4f | 1 18 | d6 | 4f |
| 50 | 1 16 | d7 | 50 |
| 51 | 1 17 | d8 | 51 |
| 52 | 1 0a | d9 | 52 |
| 53 | 1 05 | e2 | 53 |
| 54 | 1 10 | e3 | 54 |
| 55 | 1 07 | e4 | 55 |
| 56 | 1 1e | e5 | 56 |
| 57 | 1 12 | e6 | 57 |
| 58 | 1 1d | e7 | 58 |
| 59 | 1 15 | e8 | 59 |
| 5a | 1 11 | e9 | 5a |
| 5b | 4 10 | 9e | 5b |
| 5c | 4 05 | N/A | 5c |
| 5d | 4 13 | 5a | 5d |
| 5e | 4 0d | 6a | 7c |
| 5f | 4 15 | 7c | 40 |
| 60 | N/A | N/A | 60 |
| 61 | 2 03 | 81 | 61 |
| 62 | 2 19 | 82 | 62 |
| 63 | 2 0e | 83 | 63 |
| 64 | 2 09 | 84 | 64 |
| 65 | 2 01 | 85 | 65 |
| 66 | 2 0d | 86 | 66 |
| 67 | 2 1a | 87 | 67 |
| 68 | 2 14 | 88 | 68 |
| 69 | 2 06 | 89 | 69 |
| 6a | 2 0b | 91 | 6a |
| 6b | 2 0f | 92 | 6b |
| 6c | 2 13 | 93 | 6c |
| 6d | 2 1c | 94 | 6d |
| 6e | 2 0c | 95 | 6e |
| 6f | 2 18 | 96 | 6f |
| 70 | 2 16 | 97 | 70 |
| 71 | 2 17 | 98 | 71 |
| 72 | 2 0a | 99 | 72 |
| 73 | 2 05 | a2 | 73 |
| 74 | 2 10 | a3 | 74 |
| 75 | 2 07 | a4 | 75 |
| 76 | 2 1e | a5 | 76 |
| 77 | 2 12 | a6 | 77 |
| 78 | 2 1d | a7 | 78 |
| 79 | 2 15 | a8 | 79 |
| 7a | 2 11 | a9 | 7a |
| 7b | 4 0a | 9c | 7b |
| 7c | 4 1e | fe | N/A |
| 7d | 4 11 | dc | 7d |
| 7e | 4 0b | a1 | 7e |
A variety of character sets have historically been used to represent
INTERCAL programs. Atari syntax was designed
specifically for use with ASCII-7, and all Atari-syntax-based
INTERCAL compilers accept that character set as
possible input. (C-INTERCAL also accepts Latin-1 and
UTF-8.) However, the story is more complicated with Princeton syntax;
the original Princeton compiler was designed to work with EBCDIC, but
because modern computers are often not designed to work with this
character set other character sets are often used to represent it,
particularly Latin-1. The CLC-INTERCAL compiler accepts
Latin-1, a custom dialect of EBCDIC, Baudot, and a punched-card format
as input; C-INTERCAL can cope with Latin-1 Princeton
syntax, but for the other character sets, for other compilers, or just
for getting something human-readable, it’s useful to have a
conversion program. convickt is an
INTERCAL character set conversion program designed
with these needs in mind.
The syntax for using convickt is
convickt inputset outputset [padding]
(that is, the input and output character sets are compulsory, but the parameter specifying what sort of padding to use is optional).
The following values for inputset and outputset are permissible:
Latin-1, or to give it its official name ISO-8859-1, is the character set most commonly used for transmitting CLC-INTERCAL programs, and therefore nowadays the most popular character set for Princeton syntax programs. Because it is identical to ASCII-7 in all codepoints that don’t have the high bit set, most of the characters in it can be read by most modern editors and terminals. It is also far more likely to be supported by modern editors than EBCDIC, Baudot, or punched cards, all of which have fallen into relative disuse since 1972. It is also the only input character set that C-INTERCAL supports for Princeton syntax programs. It uses 8 bit characters.
EBCDIC is an 8-bit character set that was an alternative to ASCII
in 1972, and is the character set used by the original Princeton
compiler. Unfortunately, there is no single standard version; the
version of EBCDIC used by convickt is the one that
CLC-INTERCAL uses. It is the default input character
set that CLC-INTERCAL uses (although more recent
versions of CLC-INTERCAL instead try to guess the
input character set based on the input program.)
Baudot is a 5-bit character set with shift codes; therefore when
storing it in a file on an 8-bit computer, padding is needed to
fill in the remaining three bits. The standard Baudot character set
does not contain all the characters needed by
INTERCAL; therefore, CLC-INTERCAL
uses repeated shift codes to add two more sets of characters.
convickt uses the CLC-INTERCAL version of
Baudot, so as to be able to translate programs designed for that
compiler; however, standard Baudot is also accepted in input if it
contains no redundant shift codes, and if the input contains no
characters not in standard Baudot, the output will be written so
that it is both correct standard Baudot and correct
CLC-INTERCAL Baudot for those characters.
This option causes convickt to attempt a limited
conversion to or from Atari syntax; this uses ASCII-7 as the
character set, but also tries to translate between Atari and
Princeton syntax at the character level, which is sometimes but not
always effective. For instance, ? is translated from
Atari to Princeton as a yen sign, and from Princeton to Atari as a
whirlpool (@); this sort of behaviour is often capable
of translating expressions automatically, but will fail when
characters outside ASCII-7 (Atari) or Latin-1 (Princeton) are used,
and will not, for instance, translate a Princeton V,
backspace, - into Atari ?, but instead
leave it untouched. ASCII-7 is a 7-bit character set, so on an 8
bit computer, there is one bit of padding that needs to be
generated; note, however, that it is usual nowadays to clear the
top bit when transmitting ASCII-7, which the
‘printable’ and ‘zero’ padding styles will
do, but the ‘random’ style may not do.
When using a character set where not all bits in each byte are specified, a third argument can be given to specify what sort of padding to use for the top bits of each character. There are three options for this:
| Option | Meaning |
|---|---|
| printable | Keep the output in the range 32-126 where possible |
| zero | Zero the high bits in the output |
| random | Pad with random bits (avoiding all-zero bytes) |
Note that not all conversions are possible. If a character cannot be converted, it will normally be converted to a NUL byte (which is invalid in every character set); note that this will prevent round-tripping, because NUL is interpreted as end-of-input if given in the input. There is one exception; if the character that could not be converted is a tab character, it will be converted to the other character set’s representation of a space character, if possible, because the two characters have the same meaning in INTERCAL (the only difference is if the command is a syntax error that’s printed as an error message). (The exception exists to make it possible to translate existing INTERCAL source code into Baudot.)
One file in the C-INTERCAL distribution (src/idiotism.oil) is written in Optimizer Idiom Language, a programming language designed especially for expressing optimizer idioms for INTERCAL in an easily editable form (well, at least it’s easier than the unmaintainable set of idioms hard-coded in C that were used in previous versions of the INTERCAL compiler).
The structure of an OIL file consists of a sequence of idioms. An optimizer idiom looks for a certain pattern in an expression (which could be an INTERCAL expression, or an expression that has already been partly optimized and therefore contains some non-INTERCAL operators), and replaces it with a replacement that’s ‘simpler’ in some sense (in the case of C-INTERCAL, ‘simpler’ is interpreted to mean ‘compiles into a faster or smaller executable when run through a C compiler’). When an OIL program acts on an input INTERCAL file, it keeps on matching idioms to simplify expressions, until none of the idioms act any more (and if a situation occurs where idioms can keep matching indefinitely, the compiler goes into an infinite loop; so don’t allow that to happen); at present, the idioms are tried from left to right, from the leaves of an expression to its root, and from the start of the OIL file to the end; but don’t rely on that, because it’s subject to change (and gets confusing when you think about what happens when the program actually does a replacement). Anyway, the point is that if an idiom can match an expression, and another idiom doesn’t change it first, then the idiom will be matched against that part of the expression eventually, and the program won’t end until there are no idioms that match the optimized expression.
At present, the only place that OIL is used in the
C-INTERCAL compiler is when the -O option
(see -O) is used in base 2. (Syntax is
planned to extend OIL to higher bases, and some of
this is documented and even implemented, but there’s no way to
use it.) The idioms are read from the file
src/idiotism.oil during the compilation of the
C-INTERCAL from sources; you can change the idioms, but
you will then have to recompile the distribution (and if you are using
the config.sh method, also reinstall, but that will be
pretty fast.)
An OIL file is encoded as an ASCII text file using no codepoints outside the range 0-127; using 10 for newline (as on a UNIX or Linux system) is always acceptable, but using 13 then 10 (as is common on Windows or DOS) for newline is acceptable only if your C compiler recognizes that as a newline. I have no idea what happens if you use just 13 on an Apple computer on which that is the common newline convention.
Comments can be given anywhere in the file by writing lines starting
with semicolons (known as hybrids to INTERCAL
programmers). It’s also possible to write a semicolon after part
of a line to comment out the rest of the line. Inside braced C
expressions, comments can be given anywhere whitespace would be allowed
by placing them between /* and */ (in such
cases, the comments will be copied verbatim to the C temporary files
used when building the C-INTERCAL compiler, where your C
compiler will ignore them). Whitespace is ignored nearly everywhere;
the only places it isn’t ignored are in the middle of a decimal
constant, inside square brackets, immediately after one of the
characters ‘.:#_}’, and anywhere that C
doesn’t allow it in quoted C code. (This means that you can even
place it inside operators like && if you like, as long as
they’re part of OIL code and not C code, although doing this is
not recommended.) If you use whitespace in a situation where it
isn’t ignored, that’s almost certainly an error.
Idioms are grouped into groups of idioms by placing an identifier in square brackets before the group; this follows the rules for C identifiers, except that there’s a maximum length of 30 characters. This identifier is the ‘name’ of the group, which has no effect except on optimizer debug output; for that matter, the only effect a group has is that all idioms in the group look the same in optimizer debug output, because they have the same name. It’s recommended that idioms only have the same name if they are the same idiom, possibly written in several ways. For example, a shift by 0 has no effect and may as well be removed from the output; the way to express this in OIL is:
[nullshift] (_1 >> #0)->(_1) (_1 << #0)->(_1)
Here, nullshift is the name of the group of idioms, and two idioms are given; one which removes a null rightshift, and one which removes a null leftshift.
As the example above shows, the syntax of an idiom itself is
(pattern)->(replacement)
The parentheses here are actually part of the pattern and/or replacement, and as such sparks (apostrophes) or rabbit-ears (double quotes) can be used instead; they’re shown in the syntax because the outer layer of parenthesising is always required. Both the pattern and replacement are OIL expressions, although they both have their own special syntax elements as well.
An OIL expression is built around subexpressions connected by infix binary operators and/or preceded by prefix unary operators, the same way as in C or INTERCAL (although unary operators must be entirely before their argument; the one character later position is not allowed.) As in INTERCAL, there is no operator precedence; expressions must be very fully bracketed to show unambiguously what the precedences must be, and then more so; for instance, bracketing marks must be placed around the argument of a unary operator in most circumstances. Bracketing of expressions can be done with parentheses, sparks (apostrophes) or rabbit-ears (double-quotes).
The following unary and binary operators are allowed in OIL expressions:
$
|
INTERCAL mingle |
~
|
INTERCAL select |
&16
|
INTERCAL unary AND (16-bit) |
V16
|
INTERCAL unary OR (16-bit) |
?16
|
INTERCAL unary XOR (16-bit) |
^16
|
INTERCAL unary sharkfin (16-bit) |
@16
|
INTERCAL unary whirlpool (16-bit) |
@216..@516
|
INTERCAL unary generalised whirlpool (16-bit) |
&32
|
INTERCAL unary AND (32-bit) |
V32
|
INTERCAL unary OR (32-bit) |
?32
|
INTERCAL unary XOR (32-bit) |
^32
|
INTERCAL unary sharkfin (32-bit) |
@32
|
INTERCAL unary whirlpool (32-bit) |
@232..@532
|
INTERCAL unary generalised whirlpool (32-bit) |
&
|
C binary bitwise AND |
|
|
C binary bitwise OR |
^
|
C binary bitwise XOR |
+
|
C addition |
-
|
C subtraction |
*
|
C multiplication |
/
|
C integer division |
%
|
C modulus |
>
|
C greater than |
<
|
C less than |
~
|
C unary bitwise complement |
!=
|
C not equals operator |
==
|
C equals operator |
&&
|
C logical AND |
||
|
C logical OR |
>>
|
C bitwise rightshift |
<<
|
C bitwise leftshift |
!
|
C unary logical NOT |
(Note that in some cases two operators are expressed the same way, but that this doesn’t matter because one is unary and the other is binary so that there can’t be any ambiguity, only confusion. Also note that unlike INTERCAL unary logic operators, OIL unary logic operators must have a bitwidth stated.)
It hasn’t yet been explained what operands these operators have to operate on; the syntax for those depends on whether it’s a pattern or replacement that the expression is representing.
Patterns are simply OIL expressions; the expressions match either original INTERCAL input or expressions produced by earlier idioms. Each operator must match the same operator in the (possibly partially-optimised) input; the operands themselves are pattern templates specifying what operands in the input they can match.
One special simple form of match is possible:
#NUMBER, where NUMBER is in decimal,
matches a constant with that value. (Unlike in
INTERCAL, this constant is not limited to being a
onespot value; it is, however, limited to being at most twospot, as are
all operands and intermediate values in OIL.)
Otherwise, an operand consists of the following parts, written in order:
_ to specify that any data type can
be matched. In a few cases, you may want to use . or
: to specify that you only want to match a onespot or
twospot value respectively (that is, 16- or 32-bit). You can also use
#; this specifies a value that can be any width, but must
be known to be a constant with a known value at optimize time (either
because it was hardcoded as a constant originally or because a constant
was produced there by the optimizer, for instance via a constant
folding optimization).
{ and
}). This expression is written in C, not
OIL (as are all expressions in braces), and puts an
extra condition on whether the pattern matches. The exact meaning of
this will be explained later.
Note that syntax like #2 is ambiguous given what comes so
far; the first interpretation is the one that is taken in practice, and
if the second interpretation is wanted the operand should be expressed
as #{1}2, using a no-op braced expression to tell them
apart. This particular no-op is recommended because it’s detected
and optimized by the OIL compiler.
Braced expressions, which must be written purely in C, add extra conditions; they must return nonzero to allow a possible match or zero to prevent one. They can reference the following variables and functions:
c
cNUMBER
This accesses a calculation made automatically by the compiled
OIL program to identify which bits of the
operand can possibly be set, and which ones cannot be.
c by itself refers to the operand to which the braced
expression is attached; if a number is given, it refers to another
node (the number is interpreted as a reference number). The actual
value of c is a 32-bit unsigned integer, each bit of
which is true, or 1, if there is any chance that the corresponding
bit of the operand might be 1, and false, or 0, if it’s known
for certain that the corresponding bit of the operand is 0.
For instance:
_{!(c&4294901760LU)}1
The constant given here is FFFF0000 when expressed in hexadecimal;
the point is that the expression matches any operand that is known
to have a value no greater than 65535. Unless the operand is the
argument to a unary AND, this check generally makes more sense than
explicitly specifying . rather than _,
because it will identify both 16- and 32-bit values as long as
they’re small enough to fit into a onespot variable. This
code could, for instance, be used to check that an argument to a
mingle must be small enough before optimising it (this is important
because an optimisation shouldn’t optimise an error –
in this case, an overflowing mingle – into a non-error).
x
xNUMBER
x is like c, and refers to operands in
the same way, except that it can only refer to an operand marked
with #. It holds the value of that constant (a 32-bit
unsigned integer), which will be known to the optimizer at optimize
time. One common use of this is to detect whether a constant
happens to be a power of 2, although there are many other
possibilities that may be useful.
r
When inside a loop, r is the value of the loop
counter. (It’s almost certainly a mistake if you have a loop
but don’t reference the loop counter at least once, and
usually at least twice, within the loop.) See OIL Loops.
and16
and32
or16
or32
xor16
xor32
iselect
mingle
These are all functions with one argument (apart from iselect and mingle, which each take two arguments); they exist so that INTERCAL operators can be used by C expressions. They all take unsigned longs as input and output, even if they are onespot operators. Note that it’s entirely possible for these to cause a compile-time error if used on invalid arguments (such as mingling with an operand over 65535), or to silently truncate an invalid argument down to the right number of bits; both of these should be avoided if possible, so the optimiser should check first to make sure that it doesn’t use any of these functions on invalid arguments.
xselx
This function returns its argument selected with itself; so
xselx(c) is shorthand for iselect(c,c).
When the argument is very complicated, this can save a lot of space
in the original OIL program.
setbitcount
This function simply returns the number of bits with value 1 in its argument. This is sometimes useful with respect to various select-related optimisations, and can be a useful alternative to having to take logarithms in various situations.
smudgeright
smudgeleft
The smudgeright function returns its argument but with
all the bits less significant than the most significant bit with
value 1 set to 1; likewise, smudgeleft returns its
argument with all the bits more significant than the least
significant bit with value 1 set to 1.
Note that all OIL calculation is done internally
using unsigned 32-bit numbers, and C expressions you write should do
the same. The practical upshot of this is that you should write
LU after any constant you write in C code; if you
don’t do this, you are reasonably likely to get compiler
warnings, and the resulting program may not work reliably, although the
OIL compiler itself will not complain.
Here’s a more complicated example of an optimizer operand:
#{!(x&2863311530LU)&&iselect(x,1431655765LU)==
xselx(iselect(x,1431655765LU))}3
It helps to understand this if you know that 2863311530 in hexadecimal is AAAAAAAA and 1431655765 in hexadecimal is 55555555. (It’s worth putting a comment with some frequently-used decimal constants in an OIL input file to help explain what these numbers mean and make the code more maintainable.) The operand matches any constant integer which has no bits in common with AAAAAAAA, and for which if any bit in common with 55555555 is set, all less significant bits in common with that number are also set.
Replacements have much the same syntax as patterns. The expressions are
parsed in much the same way; however, one peculiarity of replacements
is that bitwidths must be specified. INTERCAL has a
typecaster that figures out whether each expression is 16 bits or 32
bits wide, but it runs before the optimizer, and as the optimizer can
produce expressions whose bitwidths don’t obey
INTERCAL’s rules, this information needs to be
inserted somehow in a replacement. In C-INTERCAL, it
usually doesn’t matter what the bitwidth is, and in cases where
it doesn’t matter the normal operators ($,
~, and so on) can be used. (The bitwidth of the entire
replacement may be different from the bitwidth of the original, thus
leading to, say, a 32-bit unary logical operation applied to a
“16-bit” argument; but this is not a problem, as it just
means that there’s an implied typecast in there somewhere.) In
cases where it does matter (due to C-INTERCAL’s
lenient interpretation of bitwidth on mingle inputs, the only place it
matters is in the input to INTERCAL unary logical
operators), both the bitwidth of the operator and the argument on which
it operates must be explicitly given, and given as the same value; to
set the bitwidth of an operator’s result, simply write the
bitwidth (16 or 32 for onespot and twospot respectively) immediately
after the operator; for instance, !=32 will generate a
not-equals operation with a 32-bit bitwidth. If an operator’s
width is set to 16, and during the course of execution of the optimized
program, a value that doesn’t fit into 16 bits is encountered,
that’s undefined behaviour and anything might happen (most
likely, though, the program will just act as though its width had been
set to 32 bits instead); this error condition is not detected. Also
note that operators like &32 already have a bitwidth
specified, so specifying &3232 (or worse,
&3216) is not allowed.
Replacement operands are simpler than pattern operands, because there are only a few forms they can take.
_NUMBER
.NUMBER
:NUMBER
This tells the optimiser to copy the operand or expression with
reference number NUMBER to this point in the replacement
used for the expression matched by the pattern. The three forms are
identical; the last two are provided for aesthetic reasons (it can
look better and be clearer to match .1 in the pattern
with .1 in the replacement, for instance). You cannot
use #NUMBER here to copy in a constant from
the left-hand side, though, nor #{1}NUMBER,
because the first means something else and the second is undefined
behaviour (that is, no behaviour for the second case has been
specifically implemented in the compiler and therefore its
behaviour is unpredictable and subject to change in future
versions); use _NUMBER to copy over a
constant with an unknown at optimizer compile time (but known at
optimize time) value from the left hand side, as you can do with
any other operand being copied.
#NUMBER
Insert a constant with the literal value NUMBER here.
#{EXPRESSION}0
Calculate the value of EXPRESSION (a C expression, which can reference the same variables and functions as a C expression in a pattern can; see C functions in OIL) and insert a constant with the calculated value here. (That is, a value is calculated at optimise-time and the resulting value is therefore constant at runtime.)
As an example, here’s an idiom that moves C bitwise AND operations inside leftshifts. (This is useful because if the optimizer has generated a large sequence of mixed ANDs and bitshifts, moving all the ANDs to one end allows them to be clumped together and optimized down to one AND, whilst the shifts can all be combined into one large shift.)
((_1 << #{1}2) & #{1}3)->((_1 & #{x3>>x2}0) << _2)
When writing idioms, sometimes instead of using very complicated expressions to try to match multiple situations at once it’s easier to have a separate idiom for each possible situation; for instance, it’s easier to write idioms for right-shift by 1, right-shift by 2, right-shift by 3, etc., rather than a general idiom to rightshift by any amount. When the idioms follow a pattern, as they will do in basically every case of this sort, it’s possible to automatically generate them using a loop. For instance, idioms to optimize a one-bit rightshift and a two-bit rightshift are:
(_1~#{xselx(x)<<1==x&&x}2)->((_1&_2)>>#1)
(_1~#{xselx(x)<<2==x&&x}2)->((_1&_2)>>#2)
Adding a loop to automatically generate the idioms, and placing a name for the group of idioms at the start, produces the following code:
[rshift]
<#1-#31
(_1~#{xselx(x)<<r==x&&x}2)->((_1&_2)>>#{r}0)
>
That’s 31 different idioms, generated with a loop. As the above
example shows, a loop starts with
<#NUMBER-#NUMBER and ends with
>; a different idiom is generated for each possible
value of the loop counter r in the range given by the
opening line of the loop. Loops must be placed around idioms, but
inside a group of idioms. Note the use of #{r}0 to
generate a constant whose value is equal to the value of the loop
counter.
Here are some tips for the best use of OIL:
MAXTOFREE in oil.y; this isn’t a limit on the
number of idioms but on the number of strings that are allocated
internally to process the idioms), and lack of error checking
(invalid OIL may produce errors in the
OIL compiler, or cause the output C code to
contain errors or warnings, or may even appear to work).
To finish off this appendix, here’s an example of the power of
OIL; this is the optimization of an idiom from the
INTERCAL-72 system library, as shown with -H;
this should give a good idea of how OIL programs
work. (All the relevant idioms are in idiotism.oil as of
the time of writing.) Note how the expression is reduced one small step
at a time; the smallness of the steps makes the optimizer more general,
because if the original expression had been slightly different, the
optimizer wouldn’t have come to the same result but could have
optimized it quite a bit of the way, up to the point where the
optimizations were no longer valid; in an older version of
INTERCAL, this idiom was simply hardcoded as a
special case and so slight variations of it weren’t optimized at
all. If you look at the idioms themselves, it’ll also be apparent
how c (the record of which bits of an expression can be 1
and which bits can’t be) is important information in being able
to apply an optimization more aggressively.
.3 <- ((((((((.3 $ 0x0) ~ (0x7fff $ 0x1)) $ 0x0) ~ (0x7fff $ 0x1)) $ 0x0) ~ (0x3fff $ 0x3)) $ 0x0) ~ (0xfff $ 0xf)) [minglefold] .3 <- ((((((((.3 $ 0x0) ~ 0x2aaaaaab) $ 0x0) ~ (0x7fff $ 0x1)) $ 0x0) ~ (0x3fff $ 0x3)) $ 0x0) ~ (0xfff $ 0xf)) [lshift16] .3 <- ((((((((((.3 >> 0x0) & 0x7fff) << 0x1) | 0x0) $ 0x0) ~ (0x7fff $ 0x1)) $ 0x0) ~ (0x3fff $ 0x3)) $ 0x0) ~ (0xfff $ 0xf)) [noopor] .3 <- (((((((((.3 >> 0x0) & 0x7fff) << 0x1) $ 0x0) ~ (0x7fff $ 0x1)) $ 0x0) ~ (0x3fff $ 0x3)) $ 0x0) ~ (0xfff $ 0xf)) [minglefold] .3 <- (((((((((.3 >> 0x0) & 0x7fff) << 0x1) $ 0x0) ~ 0x2aaaaaab) $ 0x0) ~ (0x3fff $ 0x3)) $ 0x0) ~ (0xfff $ 0xf)) [lshift16] .3 <- (((((((((((.3 >> 0x0) & 0x7fff) << 0x1) >> 0x0) & 0x7fff) << 0x1) | 0x0) $ 0x0) ~ (0x3fff $ 0x3)) $ 0x0) ~ (0xfff $ 0xf)) [noopor] .3 <- ((((((((((.3 >> 0x0) & 0x7fff) << 0x1) >> 0x0) & 0x7fff) << 0x1) $ 0x0) ~ (0x3fff $ 0x3)) $ 0x0) ~ (0xfff $ 0xf)) [minglefold] .3 <- ((((((((((.3 >> 0x0) & 0x7fff) << 0x1) >> 0x0) & 0x7fff) << 0x1) $ 0x0) ~ 0xaaaaaaf) $ 0x0) ~ (0xfff $ 0xf)) [lshift16] .3 <- ((((((((((((.3 >> 0x0) & 0x7fff) << 0x1) >> 0x0) & 0x7fff) << 0x1) >> 0x1) & 0x1fff) << 0x3) | 0x0) $ 0x0) ~ (0xfff $ 0xf)) [noopor] .3 <- (((((((((((.3 >> 0x0) & 0x7fff) << 0x1) >> 0x0) & 0x7fff) << 0x1) >> 0x1) & 0x1fff) << 0x3) $ 0x0) ~ (0xfff $ 0xf)) [minglefold] .3 <- (((((((((((.3 >> 0x0) & 0x7fff) << 0x1) >> 0x0) & 0x7fff) << 0x1) >> 0x1) & 0x1fff) << 0x3) $ 0x0) ~ 0xaaaaff) [lshift16] .3 <- (((((((((((((.3 >> 0x0) & 0x7fff) << 0x1) >> 0x0) & 0x7fff) << 0x1) >> 0x1) & 0x1fff) << 0x3) >> 0x3) & 0x1ff) << 0x7) | 0x0) [noopor] .3 <- ((((((((((((.3 >> 0x0) & 0x7fff) << 0x1) >> 0x0) & 0x7fff) << 0x1) >> 0x1) & 0x1fff) << 0x3) >> 0x3) & 0x1ff) << 0x7) [nullshift] .3 <- (((((((((((.3 & 0x7fff) << 0x1) >> 0x0) & 0x7fff) << 0x1) >> 0x1) & 0x1fff) << 0x3) >> 0x3) & 0x1ff) << 0x7) [combinelrshift] .3 <- ((((((((((.3 & 0x7fff) << 0x1) & 0x7fff) << 0x1) >> 0x1) & 0x1fff) << 0x3) >> 0x3) & 0x1ff) << 0x7) [andintolshift] .3 <- ((((((((((.3 & 0x7fff) & 0x3fff) << 0x1) << 0x1) >> 0x1) & 0x1fff) << 0x3) >> 0x3) & 0x1ff) << 0x7) [combinellshift] .3 <- (((((((((.3 & 0x7fff) & 0x3fff) << 0x2) >> 0x1) & 0x1fff) << 0x3) >> 0x3) & 0x1ff) << 0x7) [combinelrshift] .3 <- ((((((((.3 & 0x7fff) & 0x3fff) << 0x1) & 0x1fff) << 0x3) >> 0x3) & 0x1ff) << 0x7) [andintolshift] .3 <- ((((((((.3 & 0x7fff) & 0x3fff) & 0xfff) << 0x1) << 0x3) >> 0x3) & 0x1ff) << 0x7) [combinellshift] .3 <- (((((((.3 & 0x7fff) & 0x3fff) & 0xfff) << 0x4) >> 0x3) & 0x1ff) << 0x7) [combinelrshift] .3 <- ((((((.3 & 0x7fff) & 0x3fff) & 0xfff) << 0x1) & 0x1ff) << 0x7) [andintolshift] .3 <- ((((((.3 & 0x7fff) & 0x3fff) & 0xfff) & 0xff) << 0x1) << 0x7) [combinellshift] .3 <- (((((.3 & 0x7fff) & 0x3fff) & 0xfff) & 0xff) << 0x8) [combineand] .3 <- ((((.3 & 0x3fff) & 0xfff) & 0xff) << 0x8) [combineand] .3 <- (((.3 & 0xfff) & 0xff) << 0x8) [combineand] .3 <- ((.3 & 0xff) << 0x8)
The majority of the files in the C-INTERCAL distribution
are licensed under the GNU General Public License (version 2 or later),
but with some exceptions. The files ick-wrap.c and
pickwrap.c are licensed under a license that allows them
to be used for any purpose and redistributed at will, and are
explicitly not GPL’d. This means that C source code generated by
the compiler has the same copyright conditions as the original
INTERCAL source. (Note that the libraries
libick.a and libickmt.a are GPL, though, so
you cannot redistribute an executable produced by ick or
by linking a C file to either of those libraries unless the original
INTERCAL source was GPL.) For similar reasons, the
expansion libraries syslibc.c and compunex.c
are explicitly public domain. Also, this manual, and the files that are
the source code for creating it, are licensed under the GNU Free
Documentation License rather than the GPL, and the licenses themselves
(fdl-1-2.txi and COPYING.txt) are licensed
under a license that allows verbatim redistribution but not creation of
derivative works. All other files, though (including the
man pages, which are not part of this manual),
are licensed under the GPL. For the full text of the GPL, see the file
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