Calling dynamically linked Haskell code from Rust

Question

I\'m trying to compile some Rust code with some Haskell code. I have a test system set up with a file, Fibonacci.hs with a function which computes fibonacci num

Answer 1

When you compile your shared library, it looks like you need to link against libffi as well:

ghc -o libfibonacci.dylib -shared -dynamic -fPIC \
  Fibonacci.hs wrapper.c -lHSrts -lffi

I deduced this by going into my GHC library directory (/usr/local/lib/ghc-7.10.1/rts) and then grepping for the symbol ffi_call:

$ grep -lRa ffi_call .
./include/ffi.h
./rts/libHSrts-ghc7.10.1.dylib
...

I then used nm to find which exact library had it:

for i in *dylib; do
   if nm $i | grep -q 'T.*ffi_call'; then
       echo "== $i";
   fi;
done

I was then able to run with:

DYLD_LIBRARY_PATH='.' ./main

Unfortunately, it appears your code isn't quite right, as I just get a bunch of empty tuples. You forgot to have a return type on the function, and then you run into a problem that the 46th or so Fibbonacci is too big for a u32.

Additionally, you should be using the types from the libc package, and it may be safest to use a u64 here.

I have installed GHC 7.10.1 using Homebrew, but hopefully the same pattern would work elsewhere.