ghci: "GHCi runtime linker: fatal error: I found a duplicate definition for symbol"

.gitignore

*.hi
*_stub.*
ffiso

README

http://stackoverflow.com/questions/10658104/ghci-runtime-linker-issue-when-using-ffi-declarations
http://stackoverflow.com/questions/10123040/ghci-doesnt-work-with-ffi-export-declarations-shared-libaries

c.c

#include <stdio.h>

void callMeFromC(void);

void callMeFromHaskell(void)
{
	printf("callMeFromHaskell\n");
	callMeFromC();
}

FFISo.hs

{-# LANGUAGE OverloadedStrings #-}
module Main where

import qualified Data.ByteString.Char8 as B

import FFIFun.Foo

main :: IO ()
main = do
  B.putStrLn "main"
  callMeFromC
  callMeFromHaskell
  return ()

Foo.hs

{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE ForeignFunctionInterface #-}
module FFIFun.Foo where

import qualified Data.ByteString.Char8 as B

foreign import ccall "callMeFromHaskell"
  callMeFromHaskell :: IO ()

foreign export ccall callMeFromC :: IO ()
callMeFromC :: IO ()
callMeFromC = B.putStrLn "callMeFromC"

Makefile

SHELL := bash

GHC_OPT := -Wall -O2 -fno-warn-unused-do-bind


all: ffiso

test: ffiso
	./$<

ffiso: FFISo.hs c.c
	ghc --make $(GHC_OPT) $^ -o $@

clean:
	rm -rf *{.hi,o,_stub.*} ffiso FFIFun/*{.hi,.o,_stub.*}

ghci: ffiso
	ghci -package bytestring FFIFun/Foo.o c.o FFISo.hs