build.sh

rm *.o
rm test

ghclib=$(dirname $(which ghc))/../

ghc -fPIC -static -c Foo.hs
gcc -c test.c -I$ghclib/lib/ghc-8.2.2/include
ghc -o test test.o Foo.o -no-hs-main

#executation
./test

Foo.hs

{-# LANGUAGE ScopedTypeVariables #-}
module Foo where

import Foreign.Ptr (Ptr)
import Foreign.StablePtr (castStablePtrToPtr
                         ,castPtrToStablePtr
                         ,deRefStablePtr
                         ,newStablePtr
                         )

foreign export ccall foo :: IO (Ptr ())

foo :: IO (Ptr ())
foo = do
  putStrLn "I am foo!!"

  sptr <- newStablePtr (3 :: Int)
  pure $ castStablePtrToPtr sptr


foreign export ccall bar :: Ptr () -> IO ()

bar :: Ptr () -> IO ()
bar ptr = do
  value :: Int <- deRefStablePtr $ castPtrToStablePtr ptr
  print value



func :: Int -> Int
func i = i+1

foreign export ccall fooF :: IO (Ptr ())

fooF :: IO (Ptr ())
fooF = do
  putStrLn "I am foo!!"

  sptr <- newStablePtr func
  pure $ castStablePtrToPtr sptr


foreign export ccall barF :: Ptr () -> IO ()

barF :: Ptr () -> IO ()
barF ptr = do
  f :: Int -> Int <- deRefStablePtr $ castPtrToStablePtr ptr
  print (f 10)

test.c

#include "Foo_stub.h"

int main( int argc, char** argv ) {
  hs_init( &argc, &argv );
  
  void* p = foo();

  bar(p);

  void* q = fooF();

  barF(q);

  /*
  // The following segfaults.
  // 
  int(*f)(int);
  f = (int(*)(int)) fooF();

  f(4);
  */
}