hpp: A Haskell pre-processor

hpp is a Haskell pre-processor that is also a C90-compatible pre-processor (with the addition of a --cpp flag). It is packaged as both a library and an executable.

To use as a Haskell preprocessor for resolving #ifdef conditionals and macro expansion, an invocation might look like,

hpp -DDEBUG Foo.hs

To use as a C preprocessor, an invocation might look like,

hpp -DDEBUG --cpp foo.c

To have GHC use hpp as the C pre-processor, add this line to the top of a Haskell source file that makes use of the CPP LANGUAGE pragma,

{-# OPTIONS_GHC -cpp -pgmPhpp #-}

Or add this line to your .cabal file:

ghc-options: -pgmPhpp

Note that you will need to ensure that the hpp executable is available in your build environment (e.g. you can add hpp as a build-depends in your .cabal file).