Use of the Glasgow Haskell Compiler driver:

    $$ [command-line-options-and-input-files]

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This driver ($$) guides each input file through (some of the)
possible phases of a compilation:

    - unlit:	extract code from a "literate program"
    - hscpp:	run code through the C pre-processor (if -cpp flag given)
    - hsc:	run the Haskell compiler proper
    - gcc:	run the C compiler (if compiling via C)
    - as:	run the assembler
    - ld:	run the linker

For each input file, the phase to START with is determined by the
file's suffix:
    - .lhs	literate Haskell: unlit
    - .hs	illiterate Haskell: hsc
    - .hc	C from the Haskell compiler: gcc
    - .c	C not from the Haskell compiler: gcc
    - .s	assembly language: as
    - other	passed directly to the linker: ld

If no files are given on the command line, input is taken from
standard input, and processing is as for an .hs file.  (All output is
to stdout or stderr, however).

The phase at which to STOP processing is determined by a command-line
option:
    -E		stop after generating preprocessed, de-litted Haskell
		     (used in conjunction with -cpp)
    -C		stop after generating C (.hc output)
    -S		stop after generating assembler (.s output)
    -c		stop after generating object files (.o output)

Other commonly-used options are:

    -O		An `optimising' package of compiler flags, for faster code

    -prof	Compile for cost-centre profiling
		 (add -auto for automagic cost-centres on top-level functions)

    -fglasgow-exts  Allow Glasgow extensions (unboxed types, etc.)

    -H14m	Increase compiler's heap size

    -M          Output the Makefile rules recording the
		 dependencies of a list of Haskell files.
		 (ghc driver script calls upon the help of a
		  compatible mkdependHS script to do the actual
		  processing)

The User's Guide has more information about GHC's *many* options.

Given the above, here are some TYPICAL invocations of $$:

    # compile a Haskell module to a .o file, optimising:
    % $$ -c -O Foo.hs
    # link three .o files into an executable called "test":
    % $$ -o test Foo.o Bar.o Baz.o
    # compile a Haskell module to C (a .hc file), using a bigger heap:
    % $$ -C -H16m Foo.hs
    # compile Haskell-produced C (.hc) to assembly language:
    % $$ -S Foo.hc
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