Re: [Haskell-beginners] which typefor this FFI call

On 28/06/2017 15:27, PICCA Frederic-Emmanuel wrote:

my question is, when I write this

let opData = InOut $ castStablePtrToPtr statePtr

I have InOut (Ptr ()) is it possible to have somthing more like InOut (Ptr a) instead ?

Yes it's strange that `castStablePtrToPtr` returns `Ptr ()` instead of `Ptr a`. You can use `castPtr` to get the type back: let opData = InOut $ castPtr $ castStablePtrToPtr statePtr https://www.stackage.org/haddock/lts-8.20/base-4.9.1.0/Foreign-Ptr.html#v:ca... -Sylvain