Marshal.hs

{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}
module Clr.Marshal where

--
-- Conversion from a high level Haskell type a a raw bridge type
--
class Marshal a b where
  marshal :: a -> (b -> IO c) -> IO c

--
-- identity instance
--
instance {-# OVERLAPPABLE #-} (a ~ b) => Marshal a b where
  marshal x f = f x

--
-- 2-tuple instance
--
instance {-# OVERLAPS #-} (Marshal a1 b1, Marshal a2 b2) => Marshal (a1, a2) (b1, b2) where
  marshal (x1,x2) f = marshal x1 $ \x1'-> marshal x2 $ \x2'-> f (x1', x2')

--
-- 3-tuple instance
--
instance {-# OVERLAPS #-} (Marshal a1 b1, Marshal a2 b2, Marshal a3 b3) => Marshal (a1, a2, a3) (b1, b2, b3) where
  marshal (x1,x2,x3) f = marshal x1 $ \x1'-> marshal x2 $ \x2'-> marshal x3 $ \x3'-> f (x1', x2', x3')

--
-- 4-tuple instance
--
instance {-# OVERLAPS #-} (Marshal a1 b1, Marshal a2 b2, Marshal a3 b3, Marshal a4 b4) => Marshal (a1, a2, a3, a4) (b1, b2, b3, b4) where
  marshal (x1,x2,x3,x4) f = marshal x1 $ \x1'-> marshal x2 $ \x2'-> marshal x3 $ \x3'-> marshal x4 $ \x4'-> f (x1', x2', x3', x4')

--
-- 5-tuple instance
--
instance {-# OVERLAPS #-} (Marshal a1 b1, Marshal a2 b2, Marshal a3 b3, Marshal a4 b4, Marshal a5 b5) => Marshal (a1, a2, a3, a4, a5) (b1, b2, b3, b4, b5) where
  marshal (x1,x2,x3,x4,x5) f = marshal x1 $ \x1'-> marshal x2 $ \x2'-> marshal x3 $ \x3'-> marshal x4 $ \x4'-> marshal x5 $ \x5'-> f (x1', x2', x3', x4', x5')

--
-- Conversion from a raw bridge type of a methods result to a high level Haskell type
--
class Unmarshal a b where
  unmarshal :: a -> IO b

--
-- Identity instance
--
instance {-# OVERLAPPABLE #-} a ~ b => Unmarshal a b where
  unmarshal = return

--
-- If we can convert a -> IO b, then we can also convert IO a -> IO b
--
instance {-# OVERLAPPABLE #-} (Unmarshal a b) => Unmarshal (IO a) b where
  unmarshal x = x >>= \x'-> unmarshal x'