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.