Cpphs is a re-implementation of the C pre-processor that is both more
compatible with Haskell, and itself written in Haskell so that it can
be distributed with compilers.

This version of the C pre-processor is pretty-much feature-complete and
compatible with traditional (K&R) pre-processors. Additional features
include: a plain-text mode; an option to unlit literate code files,
and an option to turn off macro-expansion.