test.py

from ctypes import *
import glob
import struct
import msgpack
import itertools

# For finding where the built .so file is, independent on whether it was built with stack or cabal
def find_file_ending_with(ending_with_str, path='.'):
    # `glob` `**` does not match dotfiles (such as `.stack_work`), so we have to do that explicitly.
    glob_result_generator = itertools.chain(
        glob.glob(path + "/**/*" + ending_with_str, recursive=True),
        glob.glob(path + "/.*/**/*" + ending_with_str, recursive=True),
    )
    for path_str in glob_result_generator:
        return path_str
    else:
        raise Exception("Could not find " + ending_with_str + " in " + path)
so_file_path = find_file_ending_with('call-haskell-from-anything.so')


free = cdll.LoadLibrary("libc.so.6").free
lib = cdll.LoadLibrary(so_file_path)

lib.hs_init(0, 0)

# Set function return type to string
fun = lib.f1_t_export
fun.restype = POINTER(c_char)

# Call function
msg = msgpack.packb([1, 2.23])
length_64bits = struct.pack(">q", len(msg)) # big-endian
ptr = fun(length_64bits + msg)
data_length = struct.unpack(">q", ptr[:8])[0]
res = msgpack.unpackb(ptr[8:8+data_length])
free(ptr)

print("Haskell said:", res)


# Some shortcuts
def make_msgpack_fun(fun):
    fun.restype = POINTER(c_char)

    def f(*args):
        packed = msgpack.packb(args)
        length_64bits = struct.pack(">q", len(packed)) # big-endian
        ptr = fun(length_64bits + packed)
        data_length = struct.unpack(">q", ptr[:8])[0]
        res = msgpack.unpackb(ptr[8:8+data_length])
        free(ptr)
        return res

    return f


# Now this is the only thing required
fib = make_msgpack_fun(lib.fib_export)

print("Haskell fib:", fib(13))


# def fib(n):
#     if n == 0 or n == 1: return 1
#     return fib(n-1) + fib(n-2)

sum = 0
for x in range(100000):
    sum += fib(15)
print(sum)

lib.hs_exit()