This is a guide to using the Glasgow Haskell Compiler (GHC): an interactive and batch compilation system for the Haskell 98 language. GHC has two main components: an interactive Haskell interpreter (also known as GHCi), described in , and a batch compiler, described throughout . In fact, GHC consists of a single program which is just run with different options to provide either the interactive or the batch system. The batch compiler can be used alongside GHCi: compiled modules can be loaded into an interactive session and used in the same way as interpreted code, and in fact when using GHCi most of the library code will be pre-compiled. This means you get the best of both worlds: fast pre-compiled library code, and fast compile turnaround for the parts of your program being actively developed. GHC supports numerous language extensions, including concurrency, a foreign function interface, exceptions, type system extensions such as multi-parameter type classes, local universal and existential quantification, functional dependencies, scoped type variables and explicit unboxed types. These are all described in . GHC has a comprehensive optimiser, so when you want to Really Go For It (and you've got time to spare) GHC can produce pretty fast code. Alternatively, the default option is to compile as fast as possible while not making too much effort to optimise the generated code (although GHC probably isn't what you'd describe as a fast compiler :-). GHC's profiling system supports “cost centre stacks”: a way of seeing the profile of a Haskell program in a call-graph like structure. See for more details. GHC comes with a large collection of libraries, with everything from parser combinators to networking. The libraries are described in separate documentation. mailing lists, Glasgow Haskell Glasgow Haskell mailing lists On the World-Wide Web, there are several URLs of likely interest: Haskell home page GHC home page comp.lang.functional FAQ We run the following mailing lists about Glasgow Haskell. We encourage you to join, as you feel is appropriate. glasgow-haskell-users: This list is for GHC users to chat among themselves. If you have a specific question about GHC, please check the FAQ first (). list email address: glasgow-haskell-users@haskell.org subscribe at: http://www.haskell.org/mailman/listinfo/glasgow-haskell-users. admin email address: glasgow-haskell-users-admin@haskell.org list archives: http://www.haskell.org/pipermail/glasgow-haskell-users/ glasgow-haskell-bugs: Send bug reports for GHC to this address! The sad and lonely people who subscribe to this list will muse upon what's wrong and what you might do about it. list email address: glasgow-haskell-bugs@haskell.org subscribe at: http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs. admin email address: glasgow-haskell-bugs-admin@haskell.org list archives: http://www.haskell.org/pipermail/glasgow-haskell-bugs/ cvs-ghc: The hardcore GHC developers hang out here. This list also gets commit message from the CVS repository. There are several other similar lists for other parts of the CVS repository (eg. cvs-hslibs, cvs-happy, cvs-hdirect etc.) list email address: cvs-ghc@haskell.org subscribe at: http://www.haskell.org/mailman/listinfo/cvs-ghc. admin email address: cvs-ghc-admin@haskell.org list archives: http://www.haskell.org/pipermail/cvs-ghc/ There are several other haskell and GHC-related mailing lists served by www.haskell.org. Go to http://www.haskell.org/mailman/listinfo/ for the full list. Some Haskell-related discussion also takes place in the Usenet newsgroup comp.lang.functional. bugsreporting reporting bugs Glasgow Haskell is a changing system so there are sure to be bugs in it. To report a bug, either: Go to the SourceForge GHC page, go to the bugs section, click on submit, and enter your bug report. You can also check the outstanding bugs here and search the archives to make sure it hasn't already been reported. Or: Email your bug report to glasgow-haskell-bugs@haskell.org. Take a look at the FAQ () and , which will give you some guidance as to whether the behaviour you're seeing is really a bug or not. If it is a bug, then it might have been reported before: try searching the mailing list archives. The archives don't have a built-in search facility, but we find that Google's site search works pretty well: enter site:www.haskell.org followed by your search term into Google. If in doubt, just report it. bug reportscontents The name of the bug-reporting game is: facts, facts, facts. Don't omit them because “Oh, they won't be interested…” What kind of machine are you running on, and exactly what version of the operating system are you using? (on a Unix system, uname -a or cat /etc/motd will show the desired information.) What version of GCC are you using? gcc -v will tell you. Run the sequence of compiles/runs that caused the offending behaviour, capturing all the input/output in a “script” (a UNIX command) or in an Emacs shell window. We'd prefer to see the whole thing. Be sure any Haskell compilations are run with a -v (verbose) flag, so we can see exactly what was run, what versions of things you have, etc. What is the program behaviour that is wrong, in your opinion? If practical, please send enough source files for us to duplicate the problem. If you are a Hero and track down the problem in the compilation-system sources, please send us patches relative to a known released version of GHC, or whole files if you prefer. version, of ghc As of GHC version 6.0, we have adopted the following policy for numbering GHC versions: Stable Releases These are numbered x.y.z, where y is even, and z is the patchlevel number (the trailing .z can be omitted if z is zero). Patchlevels are bug-fix releases only, and never change the programmer interface to any system-supplied code. However, if you install a new patchlevel over an old one you will need to recompile any code that was compiled against the old libraries. The value of __GLASGOW_HASKELL__ (see ) for a major release x.y.z is the integer xyy (if y is a single digit, then a leading zero is added, so for example in version 6.2 of GHC, __GLASGOW_HASKELL__==602). __GLASGOW_HASKELL__ Snapshots/unstable releases We may make snapshot releases of the current development sources from time to time, and the current sources are always available via the CVS repository (see the GHC web site for details). Snapshot releases are named x.y.YYYYMMDD where YYYYMMDD is the date of the sources from which the snapshot was built. In theory, you can check out the exact same sources from the CVS repository using this date. If y is odd, then this is a snapshot of the CVS HEAD (the main development branch). If y is even, then it is a snapshot of the stable branch between patchlevel releases. For example, 6.3.20040225 would be a snapshot of the HEAD, but 6.2.20040225 would be a snapshot of the 6.2 branch. The value of __GLASGOW_HASKELL__ for a snapshot release is the integer xyy. You should never write any conditional code which tests for this value, however: since interfaces change on a day-to-day basis, and we don't have finer granularity in the values of __GLASGOW_HASKELL__, you should only conditionally compile using predicates which test whether __GLASGOW_HASKELL__ is equal to, later than, or earlier than a given major release. __GLASGOW_HASKELL__ The version number of your copy of GHC can be found by invoking ghc with the ––version flag (see ). &relnotes;