{-# LANGUAGE
    GADTs
  , PolyKinds
  , RankNTypes
  , ViewPatterns
  , TypeOperators
  , DeriveFunctor
  , DeriveFoldable
  , ConstraintKinds
  , TemplateHaskell
  , DeriveTraversable
  , FlexibleInstances
  , ScopedTypeVariables
  , UndecidableInstances
  , QuantifiedConstraints
  , MultiParamTypeClasses
  , UndecidableSuperClasses
  #-}
module Data.Functor.Cofree.Internal where

import Data.Monoid (Ap(..))

import Language.Haskell.TH.Syntax
import Data.DeriveLiftedInstances


kExp :: Q Exp
kExp :: Q Exp
kExp = Exp -> Q Exp
forall (f :: * -> *) a. Applicative f => a -> f a
pure (Exp -> Q Exp) -> (Name -> Exp) -> Name -> Q Exp
forall b c a. (b -> c) -> (a -> b) -> a -> c
. Name -> Exp
VarE (Name -> Q Exp) -> Name -> Q Exp
forall a b. (a -> b) -> a -> b
$ String -> Name
mkName String
"k"

kPat :: Pat
kPat :: Pat
kPat = Name -> Pat
VarP (Name -> Pat) -> Name -> Pat
forall a b. (a -> b) -> a -> b
$ String -> Name
mkName String
"k"

cofreeDeriv :: Name -> Derivator
cofreeDeriv :: Name -> Derivator
cofreeDeriv Name
cofree = Derivator
idDeriv {
  cst :: Q Exp -> Q Exp
cst = \Q Exp
e -> [| const $e $kExp |], -- Suppress "Defined but not used: ‘k’" warning
  res :: Q Exp -> Q Exp
res = \Q Exp
e -> [| $(pure (ConE cofree)) $kExp $e |],
  eff :: Q Exp -> Q Exp
eff = \Q Exp
e -> [| $(pure (ConE cofree)) $kExp <$> $e |],
  inp :: Q Pat -> Q Pat
inp = (Pat -> Pat) -> Q Pat -> Q Pat
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap (\Pat
vp -> Name -> [Pat] -> Pat
ConP Name
cofree [Pat
kPat, Pat
vp])
}

deriveCofreeInstance' :: Name -> Name -> Name -> Q [Dec]
deriveCofreeInstance' :: Name -> Name -> Name -> Q [Dec]
deriveCofreeInstance' (Type -> Q Type
forall (f :: * -> *) a. Applicative f => a -> f a
pure (Type -> Q Type) -> (Name -> Type) -> Name -> Q Type
forall b c a. (b -> c) -> (a -> b) -> a -> c
. Name -> Type
ConT -> Q Type
cofree) Name
ccofree (Type -> Q Type
forall (f :: * -> *) a. Applicative f => a -> f a
pure (Type -> Q Type) -> (Name -> Type) -> Name -> Q Type
forall b c a. (b -> c) -> (a -> b) -> a -> c
. Name -> Type
ConT -> Q Type
clss)
  = Derivator -> Q Type -> Q [Dec]
deriveInstance (Name -> Derivator
cofreeDeriv Name
ccofree)
      [t| forall a c. (c ~=> $clss) => $clss ($cofree c a) |]

class (a => b) => a :=> b
instance (a => b) => a :=> b

type a ~=> b = forall x. a x :=> b x