Minimal C main FFI example

foo.cabal

Name:                Foo
Version:             0.1.0

Homepage:            
Bug-Reports:         

Author:              John Smith
Maintainer:          John Smith <john@example.com>
Copyright:           Copyright © 2013 John Smith

License:             LGPL-3
License-File:        LICENSE.LESSER

Category:            System
Cabal-Version:       >= 1.17
Build-Type:          Simple
Tested-With:         GHC == 7.6.3

Synopsis:            

Description:

Extra-Source-Files: LICENSE

Executable foo
  Default-Language:     Haskell2010
  GHC-Options:          -Wall -threaded -no-hs-main
  GHC-Prof-Options:     -auto-all -caf-all -rtsopts
  Main-Is:              main.c
  Other-Modules:        Foo

  C-Sources:            
  CC-Options:           -Wall -Wextra -pedantic -strict -std=c99

  Build-Depends:        base

Foo.hs

{-# LANGUAGE ForeignFunctionInterface #-}
module Foo where

import Foreign.C.String
import Foreign.C.Types

foreign export ccall start_server :: CInt -> CString -> IO ()
foreign export ccall start_client :: CString -> IO ()

start_server :: CInt -> CString -> IO ()
start_server pid = undefined

start_client :: CString -> IO ()
start_client = undefined

main.c

#include <HsFFI.h>
#ifdef __GLASGOW_HASKELL__
#include "Foo_stub.h"
extern void __stginit_Foo(void);
#endif

int
main(int argc, char **argv)
{
    hs_init(&argc, &argv);
#ifdef __GLASGOW_HASKELL__
    hs_add_root(__stginit_Foo);
#endif

/* call functions defined in module Foo.hs here */

    hs_exit();

    return 0;
}