Statically link C++ library with a Haskell library

Question

Setup: I have a Haskell library HLib which makes calls to a C/C++ backend CLib for efficiency. The backend is small and specialized for use with

Answer 1

Including a C or C++ library with a Haskell library is trivial once you know a few tricks.

I got the core from this article, though it seems to overcomplicate things. You can use cabal (currently 1.25) with a Simple build type (i.e. no special Setup.hs), no makefile, and no external tools like c2hs.

To include symbols from a pure C library:

1. In your cabal file, either add Include-dirs: relative/path/to/headers/ or Includes: relative/path/to/myheader.h.
2. Add C-sources: relative/path/to/csources/c1.c, relative/path/to/csources/c2.c, etc.

There's a couple of extra bits for C++:

3. You can add .cpp files to the C-sources field in the cabal file.
4. On all functions in .cpp files that Haskell needs access to, add extern "C" to avoid name mangling.
5. Surround all non-pure-C code in header files with #ifdef __cplusplus ... #endif (see n.m.'s answer).
6. If you use the standard C++ library, you'll need to add extra-libraries: stdc++ to your cabal file, and link with g++ using ghc-options: -pgmlg++.
7. You may have to fiddle a bit with the order that you list the .c(pp) files in the cabal file if you want dynamic linking (i.e. cabal repl) to work. See this ticket for more information.

That's it! You can see a complete working example here which works with both stack and cabal.