{-# LANGUAGE FlexibleInstances, MultiParamTypeClasses, FunctionalDependencies, UndecidableInstances #-}
{- |
   The HList library

   (C) 2004, Oleg Kiselyov, Ralf Laemmel, Keean Schupke

   A generic implementation of a type-safe cast. The specific coding
   here is only shown for completeness' sake and it is explained in the
   TR version of the paper. The shown coding does not rely on separate
   compilation (while "Data.HList.TypeCastGeneric1" does), but on some other
   tricks.
-}

module Data.HList.TypeCastGeneric3 where

import Data.HList.FakePrelude


{-----------------------------------------------------------------------------}

-- The actual encoding

-- The class TypeCast is declared in FakePrelude.
-- class TypeCast   a b   | a -> b, b->a   where typeCast   :: a -> b
class TypeCast'  t a b | t a -> b, t b -> a where typeCast'  :: t->a->b
class TypeCast'' t a b | t a -> b, t b -> a where typeCast'' :: t->a->b
instance TypeCast'  () a b => TypeCast a b where typeCast x = typeCast' () x
instance TypeCast'' t a b => TypeCast' t a b where typeCast' = typeCast''
instance TypeCast'' () a a where typeCast'' _ x  = x


{-----------------------------------------------------------------------------}