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1. Introduction to GHC

This is a guide to using the Glasgow Haskell compilation (GHC) system. It is a batch compiler for the Haskell 1.4 language, with support for various Glasgow-only extensions.

Many people will use GHC very simply: compile some modules---ghc -c -O Foo.hs Bar.hs; and link them--- ghc -o wiggle -O Foo.o Bar.o.

But if you need to do something more complicated, GHC can do that, too:

ghc -c -O -fno-foldr-build -dcore-lint -fvia-C -ddump-simpl Foo.lhs
Stay tuned---all will be revealed!

In this document, we assume that GHC has been installed at your site as ghc. The rest of this section provide some tutorial information on batch-style compilation; if you're familiar with these concepts already, then feel free to skip to the next section.

1.1 The (batch) compilation system components

The Glorious Haskell Compilation System, as with most UNIX (batch) compilation systems, has several interacting parts:

  1. A driver ghc ---which you usually think of as ``the compiler''---is a program that merely invokes/glues-together the other pieces of the system (listed below), passing the right options to each, slurping in the right libraries, etc.
  2. A literate pre-processor unlit that extracts Haskell code from a literate script; used if you believe in that sort of thing.
  3. The Haskellised C pre-processor hscpp, only needed by people requiring conditional compilation, probably for large systems. The ``Haskellised'' part just means that #line directives in the output have been converted into proper Haskell {-# LINE ... -} pragmas. You must give an explicit -cpp option for the C pre-processor to be invoked.
  4. The Haskell compiler hsc, which---in normal use---takes its input from the C pre-processor and produces assembly-language output (sometimes: ANSI C output).
  5. The ANSI C Haskell high-level assembler :-) compiles hsc's C output into assembly language for a particular target architecture. In fact, the only C compiler we currently support is gcc, because we make use of certain extensions to the C language only supported by gcc. Version 2.x is a must; we recommend version for stability (we've heard both good and bad reports of later versions).
  6. The assembler ---a standard UNIX one, probably as .
  7. The linker ---a standard UNIX one, probably ld.
  8. A runtime system, including (most notably) a storage manager; the linker links in the code for this.
  9. The Haskell standard prelude , a large library of standard functions, is linked in as well.
  10. Parts of other installed libraries that you have at your site may be linked in also.

1.2 What really happens when I ``compile'' a Haskell program?

You invoke the Glasgow Haskell compilation system through the driver program ghc. For example, if you had typed a literate ``Hello, world!'' program into hello.lhs, and you then invoked:

ghc hello.lhs

the following would happen:

  1. The file hello.lhs is run through the literate-program code extractor unlit , feeding its output to
  2. The Haskell compiler proper hsc , which produces input for
  3. The assembler (or that ubiquitous ``high-level assembler,'' a C compiler), which produces an object file and passes it to
  4. The linker, which links your code with the appropriate libraries (including the standard prelude), producing an executable program in the default output file named a.out.

You have considerable control over the compilation process. You feed command-line arguments (call them ``options,'' for short) to the driver, ghc; the ``types'' of the input files (as encoded in their names' suffixes) also matter.

Here's hoping this is enough background so that you can read the rest of this guide!

1.3 Meta-information: Web sites, mailing lists, etc.

On the World-Wide Web, there are several URLs of likely interest:

We run two mailing lists about Glasgow Haskell. We encourage you to join, as you feel is appropriate.


This list is for GHC users to chat among themselves. Subscribe by sending mail to, with a message body (not header) like this:

subscribe glasgow-haskell-users MyName <> 

(The last bit is your all-important e-mail address, of course.)

To communicate with your fellow users, send mail to

To contact the list administrator, send mail to An archive of the list is available on the Web: glasgow-haskell-users mailing list archive.


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.

Subscribe via with:

subscribe glasgow-haskell-bugs My Name <>

Again, you may contact the list administrator at And, yes, an archive of the list is available on the Web at: : glasgow-haskell-bugs mailing list archive

There is also the general Haskell mailing list. Subscribe by sending email to, with the usual message body:

subscribe haskell My Name <>

Some Haskell-related discussion takes place in the Usenet newsgroup comp.lang.functional. (But note: news is basically dead at Glasgow. That's one reason Glaswegians aren't too active in c.f.l.)

The main anonymous-FTP site for Glasgow Haskell is ``Important'' bits are mirrored at other Haskell archive sites (and we have their stuff, too).

1.4 Release notes for version 4.04---7/99

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