ts.hs

{-# LANGUAGE MagicHash #-}
{-# LANGUAGE UnboxedTuples #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE TypeInType #-}

-- | Conversion between unlifted and lifted datatypes
module Packed.Levity
  ( -- * Types
    Rep
  , Levity(..)
  ) where

import Data.Kind (Type)
import GHC.Types (TYPE, RuntimeRep(..), Int(..), Word(..))
import GHC.Exts  (Int#, Word#, ByteArray#)

type family Rep (a :: Type) :: RuntimeRep

type instance Rep Int = IntRep
type instance Rep Word = WordRep

type Stuff# = (# Int#, Int# #)

data Stuff = Stuff Int# Int#

type instance Rep Stuff = TupleRep '[ 'IntRep, 'IntRep ]

stuff# :: (# Int#, Int# #) -> Stuff
stuff# (# x, y #) = Stuff x y

unStuff# :: Stuff -> (# Int#, Int# #)
unStuff# (Stuff x y) = (# x, y #)
class Levity (a :: Type) where
  type Unlifted a :: TYPE (Rep a)
  box   :: Unlifted a -> a
  unbox :: a -> Unlifted a

instance Levity Int where
  type Unlifted Int = Int#
  box = I#
  unbox (I# i) = i

instance Levity Word where
  type Unlifted Word = Word#
  box = W#
  unbox (W# w) = w

instance Levity Stuff where
  type Unlifted Stuff = Stuff#
  box = stuff#
  unbox = unStuff#