Small example of compiling a Haskell Mac .dylib to be used from C

Adder.hs

{-# LANGUAGE ForeignFunctionInterface #-}
module Adder where

import Foreign.C

adder :: CInt -> CInt -> IO CInt
adder x y = return $ x + y

foreign export ccall adder :: CInt -> CInt -> IO CInt

build.sh

#!/bin/bash
ghc -o libadder.dylib -shared -static -fPIC Adder.hs StartEnd.c -lHSrts -lCffi
# -shared means to make a dylib.
# -static means use the static versions of ghc stuff.
# -lCffi links the static libCffi.a; -lffi would link the dynamic libffi.dylib
#   ^ look inside $(ghc --print-libdir)/rts for details
gcc -o main main.c libadder.dylib -I"$(ghc --print-libdir)/include"
# alternatively, you can copy the headers into here like so:
#   cp -R "$(ghc --print-libdir)/include"/* .
#   gcc -o main main.c libadder.dylib
install_name_tool -change "@rpath/libadder.dylib" "@executable_path/libadder.dylib" main

main.c

#include "Adder_stub.h"
#include <stdio.h>

void HsStart(void);
void HsEnd(void);

int main()
{
  HsStart();
  printf("12 + 5 = %i\n", adder(12,5));
  HsEnd();
  return 0;
}

StartEnd.c

#include <stdlib.h>
#include "HsFFI.h"

void HsStart(void) {
  hs_init(NULL, NULL);
}

void HsEnd(void) {
  hs_exit();
}