GHC Commentary: Top-level orgainsation of GHC
The GHC API is the interface exported by compiler/main/GHC.hs. To compile a Haskell module that uses the GHC API, use the flag -package ghc (in GHC 6.6 and later). GHC itself contains a few front-ends:
- The "one-shot" mode, where GHC compiles each file on the command line separately (eg. ghc -c Foo.hs). This mode is implemented directly on top of HscMain, since it compiles only one file at a time. In fact, this is all that GHC consisted of prior to version 5.00 when GHCi and --make were introduced.
- GHCi, the interactive environment, is implemented in compiler/ghci/InteractiveUI.hs and sits squarely on top of the GHC API.
- --make is almost a trivial client of the GHC API, and is implemented in compiler/main/Main.hs.
- -M, the Makefile dependency generator, is also a client of the GHC API and is implemented in compiler/main/DriverMkDepend.hs.
Note that since GHC is packaged as a single binary, all of these front-ends are present, and there is a single command-line interface implemented in compiler/main/Main.hs.