Calling Haskell functions from Python

Question

I want to use some Haskell libraries (e.g. Darcs, Pandoc) from Python, but it seems there’s no direct foreign function interface to Haskell in Python. Is there any way to do

Answer 1

There is a wrapper that allows one to call Haskell functions from Python here:

https://github.com/sakana/HaPy

From a cursory inspection, it seems to require that the Haskell functions have relatively simple type signatures (basically, all the types involved had better be things like Int and Float which c knows about, or lists of things of this form, or lists of lists, or so on).

An example is provided where one has this Haskell code:

module ExampleModule where

import Data.Char

foo :: Double -> Double -> Double
foo = (*)

bar :: Int -> Int
bar i = sum [1..i]

baz :: Int -> Bool
baz = (> 5)

arr_arg :: [Int] -> Int
arr_arg = sum

arr_ret :: Int -> [Int]
arr_ret i = [1..i]

arr_complex :: [[Int]] -> [[Int]]
arr_complex = map (map (* 2))

string_fun :: String -> String
string_fun str = str ++ reverse str

char_test :: Char -> Int
char_test = ord

and one accesses it like this:

from HaPy import ExampleModule

print "3 * 7 is", ExampleModule.foo(3,7)
print "sum from 1 to 10 is", ExampleModule.bar(10)
print "3 > 5 is", ExampleModule.baz(3)

print "sum from 1 to 100 is", ExampleModule.arr_arg(range(101))
print "numbers from 1 to 10 are", ExampleModule.arr_ret(10)

print "complex array passing:", ExampleModule.arr_complex([range(3), [], range(100)])
print "string fun:", ExampleModule.string_fun("This isn't really a palindrome.")

s = ExampleModule.string_fun("abc\000def")
print "string fun with nulls:", s,
for c in s:
    print ord(c),
print

print "char test:", ExampleModule.char_test("t")

Unfortunately, you do need to do some export plumbing on the Haskell side.