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

Question

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?

Answer 1

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