Re: [Haskell-cafe] Anonymous FFI calls

Quoth Sylvain Henry ,

2015-02-11 16:18 GMT+01:00 Francesco Mazzoli :

...

Relatedly, if I have some function pointer known at runtime that addresses a C function that takes some arguments, I have no way to invoke it from Haskell, since all FFI imports must be declared at compile-time, and I don't know the address of the symbol I want to execute at compile time.

You can use FunPtr and wrapper imports to convert a FunPtr into a Haskell function.

For example, foreign import ccall "get_type1_fn" get_type1_fn :: IO (FunPtr (CInt -> IO CInt)) foreign import ccall "dynamic" type1FunPtrToFun :: FunPtr (CInt -> IO CInt) -> (CInt -> IO CInt) main = do fp <- get_type1_fn let f = type1FunPtrToFun fp f 5 >>= print I guess the key point in this demo is that a C function is able to return a FunPtr. Donn