Chapter 1. Introduction to GHC

Table of Contents
1.1. The (batch) compilation system components
1.2. What really happens when I “compile” a Haskell program?
1.3. Meta-information: Web sites, mailing lists, etc.
1.4. Release notes for version 4.06—1/00

This is a guide to using the Glasgow Haskell compilation (GHC) system. It is a batch compiler for the Haskell 98 language, with support for various Glasgow-only extensions. In this document, we assume that GHC has been installed at your site as ghc. A separate document, “Building and Installing the Glasgow Functional Programming Tools Suite”, describes how to install ghc.

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!

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.