cpphs binary package in Ubuntu Focal amd64

 The C pre-processor has been widely used in Haskell source code. It
 enables conditional compilation for different compilers, different
 versions of the same compiler, and different OS platforms. It is also
 occasionally used for its macro language, which can enable certain
 forms of platform-specific detail-filling, such as the tedious
 boilerplate generation of instance definitions and FFI declarations.
 .
 However, gcc's cpp has recently been evolving to more strictly adhere
 to the C standard. This has had the effect of making it increasingly
 incompatible with Haskell's syntax. This is a cpp-a-like designed with
 Haskell's syntax in mind.

Source package