Hello, Is calling haskell from C from haskell possible? This is what i tried (generated with green-card):
It ought to work. Instead of using Greencard (which only supports Haskell->C) or the old _casm_ operation, I'd recommend using the new foreign function interface. http://www.cse.unsw.edu.au/~chak/haskell/ffi/ In particular you should look at 'foreign import' (for Haskell->C calls) and 'foreign export' or 'foreign import wrapper' (for C -> Haskell calls). I'm attaching part of the Hugs test suite which shows how to use 'foreign import' and 'foreign import wrapper' to call from Haskell -> C -> Haskell. Benefits of using the ffi are that your code will be portable to other compilers (Hugs and NHC) and you'll be in well charted waters where you can be confident that if things don't work then you've found a bug and not an undocumented feature. -- Alastair Reid alastair@reid-consulting-uk.ltd.uk Reid Consulting (UK) Limited http://www.reid-consulting-uk.ltd.uk/alastair/ Here's part of the Hugs test suite (hugs98/tests/ffi/Sin.hs). The most relevant example is the third test which creates and uses sin_addr2. -- !!! Testing static, dynamic and wrapped import of trig function -- Imports kept minimal to avoid pulling in Storable and other -- things which use even more ffi. import IOExts( unsafePerformIO ) import Ptr( FunPtr, freeHaskellFunPtr ) tests = do putStrLn "\nTesting sin==mysin (should return lots of Trues)" print (testSin sin mysin) putStrLn "\nTesting sin==dynamic_sin (should return lots of Trues)" print (testSin sin (dyn_sin sin_addr)) putStrLn "\nTesting sin==IO wrapped_sin (should return lots of Trues)" sin_addr2 <- wrapIO (return . sin) print (testSin sin (unsafePerformIO . (dyn_sinIO sin_addr2))) freeHaskellFunPtr sin_addr2 putStrLn "\nTesting sin==Id wrapped_sin (should return lots of Trues)" sin_addr3 <- wrapId sin print (testSin sin (dyn_sin sin_addr3)) freeHaskellFunPtr sin_addr3 testSin f g = [ (f x == g x) | x <- [0,0.01 .. 1] ] foreign import ccall "math.h sin" mysin :: Double -> Double foreign import ccall "dynamic" dyn_sin :: FunPtr (Double -> Double) -> (Double -> Double) foreign import ccall "dynamic" dyn_sinIO :: FunPtr (Double -> IO Double) -> (Double -> IO Double) foreign import ccall "math.h &sin" sin_addr :: FunPtr (Double -> Double) foreign import ccall "wrapper" wrapId :: (Double -> Double) -> IO (FunPtr (Double -> Double)) foreign import ccall "wrapper" wrapIO :: (Double -> IO Double) -> IO (FunPtr (Double -> IO Double))