How is Foreign Function Interface (FFI) used with Stack?

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I was following some FFI tutorials and examples (here and here), and I was wondering what should change when using stack?

In the examples, the source C file is compiled to an object file using gcc -c -o termops.o termops.c and included in the gcc compilation using ghc --make -main-is FfiEx -o ffi_ex FfiEx.hs termops.o. How can the equivalent be accomplished using stack?

haskell-stack ffi c haskell
1 Answers

Here is as minimal an FFI C project as I could imagine.

$ cd c-proj
c-proj$ ls
Main.hs      c-proj.cabal c_file.c

The contents of these files:

  • c-proj.cabal: describes the 

    name:            c-proj
version:         0.1.0.0
cabal-version:   >= 1.22
build-type:      Simple

executable main
  main-is:       Main.hs
  build-depends: base >= 4.9
  c-sources:     c_file.c

  • Main.hs: the only Haskell source file

    {-# LANGUAGE ForeignFunctionInterface #-}

module Main where

foreign import ccall "plus_ten" plusTen :: Int -> IO Int

main = do
  n <- plusTen 2
  print n

  • c_file.c: the C source file

    #include<stdio.h>

int plus_ten(int n) {
  printf("%d + 10\n", n);
  return n + 10;
}

Then, if you want to use Stack, you can run stack init.

$ stack init
<< Shell output snipped >>
$ stack build
<< Shell output snipped >>
$ stack exec main
2 + 10
12
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