Skip to content

Instantly share code, notes, and snippets.

@ijt
Created May 11, 2011 07:19
Show Gist options
  • Save ijt/966037 to your computer and use it in GitHub Desktop.
Save ijt/966037 to your computer and use it in GitHub Desktop.
Example of calling C from Haskell using the FFI
{-# LANGUAGE ForeignFunctionInterface #-}
-- Simple example of calling C from Haskell.
--
-- $ ghci
-- > :load FfiExample.hs
-- > c_sin pi
-- 1.2246467991473532e-16
--
-- $ ghc --make FfiExample.hs
-- $ ./FfiExample
module Main where
import Foreign
import Foreign.C.Types
import Foreign.C.String
import Text.Printf
-- http://book.realworldhaskell.org/read/interfacing-with-c-the-ffi.html
foreign import ccall "math.h sin"
c_sin :: CDouble -> CDouble
foreign import ccall "stdlib.h system"
c_system :: CString -> IO CInt
sin2 :: Double -> Double
sin2 x =
realToFrac $ c_sin $ realToFrac x
system :: String -> IO CInt
system cmd =
withCString cmd c_system
main = do
putStrLn (printf "sin 3.14 = %.3f" (sin2 3.14))
putStrLn "ls:"
system "ls"
return ()
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment