Exporting own "data" type

[manzznam]

I am trying to export a module with own types with the following code:

{-# LANGUAGE ForeignFunctionInterface #-}
{-# LANGUAGE TemplateHaskell #-}

module RectangleMover where

import Foreign.C
import FFI.Anything.TypeUncurry.Msgpack

data Point = Point Int Int
movePoint :: Point -> Int -> Int -> Point
movePoint (Point x y) dx dy = Point (x + dx) (y + dy)

data Rectangle = Rectangle { corner :: Point, width :: Int, height :: Int }
move :: Rectangle -> Int -> Int -> Rectangle
move r@(Rectangle {corner=c}) dx dy = r { corner = movePoint c dx dy }

foreign export ccall move_export :: CString -> IO CString
move_export :: CString -> IO CString
move_export = export move

But when i try to compile this i get the this error message:

[1 of 1] Compiling RectangleMover ( test.hs, test.o )

test.hs:19:15:
No instance for (Data.MessagePack.Object.MessagePack Rectangle)
arising from a use of ‘export’
In the expression: export move
In an equation for ‘move_export’: move_export = export move

What am i missing? Or does this package support exporting own types at all?

[abooij]

export :: (MSG.MessagePack (TypeList l), ToTypeList f l r, MSG.MessagePack r) => f -> CString -> IO CString

In other words, the type constituents of f (in other words, the respective types of its inputs and outputs) have to be instances of MessagePack (see the msgpack package). Your Rectangle type is missing such an instance.