{-# LANGUAGE ConstraintKinds       #-}
{-# LANGUAGE FlexibleContexts      #-}
{-# LANGUAGE FlexibleInstances     #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE TypeOperators         #-}
{-# LANGUAGE UndecidableInstances  #-}
--------------------------------------------------------------------------------
-- |
-- Module      :  Data.Comp.Desugar
-- Copyright   :  (c) 2011 Patrick Bahr, Tom Hvitved
-- License     :  BSD3
-- Maintainer  :  Tom Hvitved <hvitved@diku.dk>
-- Stability   :  experimental
-- Portability :  non-portable (GHC Extensions)
--
-- This modules defines the 'Desugar' type class for desugaring of terms.
--
--------------------------------------------------------------------------------

module Data.Comp.Desugar where

import Data.Comp

-- |The desugaring term homomorphism.
class (Functor f, Functor g) => Desugar f g where
    desugHom :: Hom f g
    desugHom = forall (f :: * -> *) (g :: * -> *) a.
Desugar f g =>
Alg f (Context g a)
desugHom' forall b c a. (b -> c) -> (a -> b) -> a -> c
. forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap forall c (b :: * -> *). c -> Cxt Hole b c
Hole
    desugHom' :: Alg f (Context g a)
    desugHom' f (Context g a)
x = forall (f :: * -> *) h a.
Functor f =>
Context f (Cxt h f a) -> Cxt h f a
appCxt (forall (f :: * -> *) (g :: * -> *). Desugar f g => Hom f g
desugHom f (Context g a)
x)

-- We make the lifting to sums explicit in order to make the Desugar
-- class work with the default instance declaration further below.
instance {-# OVERLAPPABLE #-} (Desugar f h, Desugar g h) => Desugar (f :+: g) h where
    desugHom :: Hom (f :+: g) h
desugHom = forall {k} (f :: k -> *) (a :: k) b (g :: k -> *).
(f a -> b) -> (g a -> b) -> (:+:) f g a -> b
caseF forall (f :: * -> *) (g :: * -> *). Desugar f g => Hom f g
desugHom forall (f :: * -> *) (g :: * -> *). Desugar f g => Hom f g
desugHom

-- |Desugar a term.
desugar :: Desugar f g => Term f -> Term g
{-# INLINE desugar #-}
desugar :: forall (f :: * -> *) (g :: * -> *). Desugar f g => Term f -> Term g
desugar = forall (f :: * -> *) (g :: * -> *).
(Functor f, Functor g) =>
Hom f g -> CxtFun f g
appHom forall (f :: * -> *) (g :: * -> *). Desugar f g => Hom f g
desugHom

-- |Lift desugaring to annotated terms.
desugarA :: (Functor f', Functor g', DistAnn f p f', DistAnn g p g',
             Desugar f g) => Term f' -> Term g'
desugarA :: forall (f' :: * -> *) (g' :: * -> *) (f :: * -> *) p (g :: * -> *).
(Functor f', Functor g', DistAnn f p f', DistAnn g p g',
 Desugar f g) =>
Term f' -> Term g'
desugarA = forall (f :: * -> *) (g :: * -> *).
(Functor f, Functor g) =>
Hom f g -> CxtFun f g
appHom (forall (f :: * -> *) p (f' :: * -> *) (g :: * -> *) (g' :: * -> *).
(DistAnn f p f', DistAnn g p g', Functor g) =>
Hom f g -> Hom f' g'
propAnn forall (f :: * -> *) (g :: * -> *). Desugar f g => Hom f g
desugHom)

-- |Default desugaring instance.
instance {-# OVERLAPPABLE #-} (Functor f, Functor g, f :<: g) => Desugar f g where
    desugHom :: Hom f g
desugHom = forall (f :: * -> *) a. Functor f => f a -> Context f a
simpCxt forall b c a. (b -> c) -> (a -> b) -> a -> c
. forall (f :: * -> *) (g :: * -> *) a. (f :<: g) => f a -> g a
inj