RankNTypes.hs

{-# LANGUAGE CPP                #-}
{-# LANGUAGE FlexibleInstances  #-}
{-# LANGUAGE OverloadedStrings  #-}
{-# LANGUAGE RankNTypes         #-}
{-# LANGUAGE StandaloneDeriving #-}
{-# LANGUAGE TemplateHaskell    #-}
{-# LANGUAGE TypeFamilies       #-}
{-# OPTIONS_GHC -fno-warn-orphans        #-}
{-# OPTIONS_GHC -fno-warn-name-shadowing #-}

{-|
Module:      Derived.RankNTypes
Copyright:   (C) 2014-2015 Ryan Scott
License:     BSD-style (see the file LICENSE)
Maintainer:  Ryan Scott
Stability:   Provisional
Portability: GHC

Defines data types with rank-n voodoo.
-}
module Derived.RankNTypes (TyCon(..), TyFamily(..)) where

import Prelude ()
import Prelude.Compat hiding (Show(..))

import Test.QuickCheck (Arbitrary(..))

import Text.Show as S (Show(..))
import Text.Show.Text as T (Show(..), Show1(..), Show2(..))
import Text.Show.Text.TH (deriveShow, deriveShow1, deriveShow2,
                          mkShowbPrec, mkShowbPrecWith, mkShowbPrecWith2)

import TransformersCompat as S (Show1(..), Show2(..), showsUnaryWith, showsBinaryWith)

-------------------------------------------------------------------------------

data TyCon a b = TyCon (forall a. Tagged2 a Int b)
                       (forall b. Tagged2 b a   a)

deriving instance (S.Show a, S.Show b) => S.Show (TyCon a b)

-------------------------------------------------------------------------------

data family TyFamily
#if __GLASGOW_HASKELL__ >= 708 && __GLASGOW_HASKELL__ < 710
                     a b :: *
#else
                     x y :: *
#endif

data instance TyFamily a b = TyFamily (forall a. Tagged2 a Int b)
                                      (forall b. Tagged2 b a   a)

deriving instance (S.Show a, S.Show b) => S.Show (TyFamily a b)

-------------------------------------------------------------------------------

newtype Tagged2 s t c = Tagged2 c
  deriving S.Show

-------------------------------------------------------------------------------

-- There's so much rank-n voodoo going on that we can't have a more generalized
-- Arbitrary instances. Oh well, this is close enough.
instance Arbitrary (TyCon Int Int) where
    arbitrary = do
        i1 <- arbitrary
        i2 <- arbitrary
        pure $ TyCon (Tagged2 i1) (Tagged2 i2)

instance Arbitrary (TyFamily Int Int) where
    arbitrary = do
        i1 <- arbitrary
        i2 <- arbitrary
        pure $ TyFamily (Tagged2 i1) (Tagged2 i2)

-------------------------------------------------------------------------------

instance S.Show a => S.Show1 (TyCon a) where
    showsPrecWith = showsPrecWith2 showsPrec
instance S.Show2 TyCon where
    showsPrecWith2 sp1 sp2 p (TyCon b a) =
        showsForall sp1 sp2 "TyCon" p b a

instance S.Show a => S.Show1 (TyFamily a) where
    showsPrecWith = showsPrecWith2 showsPrec
instance S.Show2 TyFamily where
    showsPrecWith2 sp1 sp2 p (TyFamily b a) =
        showsForall sp1 sp2 "TyFamily" p b a

showsForall :: (Int -> a -> ShowS) -> (Int -> b -> ShowS)
            -> String -> Int
            -> (forall a. Tagged2 a Int b)
            -> (forall b. Tagged2 b a a)
            -> ShowS
showsForall sp1 sp2 name p b a =
        showsBinaryWith (showsPrecWith2 showsPrec sp2)
                        (showsPrecWith2 sp1       sp1)
                        name p b a

-------------------------------------------------------------------------------

$(deriveShow  ''TyCon)
$(deriveShow1 ''TyCon)
$(deriveShow2 ''TyCon)

#if MIN_VERSION_template_haskell(2,7,0)
$(deriveShow  'TyFamily)
$(deriveShow1 'TyFamily)
$(deriveShow2 'TyFamily)
#endif

-------------------------------------------------------------------------------

$(return [])

instance S.Show1 (Tagged2 s t) where
    showsPrecWith sp p (Tagged2 b) = showsUnaryWith sp "Tagged2" p b

instance S.Show2 (Tagged2 s) where
    showsPrecWith2 _ = showsPrecWith

instance T.Show c => T.Show (Tagged2 s t c) where
    showbPrec = $(mkShowbPrec ''Tagged2)

instance T.Show1 (Tagged2 s t) where
    showbPrecWith = $(mkShowbPrecWith ''Tagged2)

instance T.Show2 (Tagged2 s) where
    showbPrecWith2 = $(mkShowbPrecWith2 ''Tagged2)