Church.hs

{-# LANGUAGE DerivingVia #-}

-- This Source Code Form is subject to the terms of the Mozilla Public
-- License, v. 2.0. If a copy of the MPL was not distributed with this
-- file, You can obtain one at https://mozilla.org/MPL/2.0/.

{- |
Copyright   :  (c) 2023 Yamada Ryo
License     :  MPL-2.0 (see the file LICENSE)
Maintainer  :  ymdfield@outlook.jp
Stability   :  experimental
Portability :  portable

A Church-encoded Freer transformer.
-}
module Control.Monad.Trans.Freer.Church where

import Control.Effect.Class (Instruction, LiftIns (..))
import Control.Freer.Trans (TransFreer (hoistFreer, liftInsT, liftLowerFT, runInterpretF))
import Control.Heftia.Trans (TransHeftia (..), liftSigT)
import Control.Monad.Trans (MonadTrans)
import Control.Monad.Trans.Freer (
    MonadTransFreer (interpretMK, reinterpretMK),
    ViaLiftLower (ViaLiftLower),
 )
import Control.Monad.Trans.Heftia.Church (HeftiaChurchT (HeftiaChurchT))

-- | A Church-encoded Freer transformer.
newtype FreerChurchT (ins :: Instruction) f a = FreerChurchT
    {unFreerChurchT :: HeftiaChurchT (LiftIns ins) f a}

deriving newtype instance Functor (FreerChurchT ins m)
deriving newtype instance Applicative (FreerChurchT ins m)
deriving newtype instance Monad (FreerChurchT ins m)

instance TransFreer Monad FreerChurchT where
    liftInsT = FreerChurchT . liftSigT . LiftIns
    {-# INLINE liftInsT #-}

    liftLowerFT = FreerChurchT . liftLowerHT
    {-# INLINE liftLowerFT #-}

    runInterpretF i = runElaborateH (i . unliftIns) . unFreerChurchT
    {-# INLINE runInterpretF #-}

    hoistFreer phi = FreerChurchT . hoistHeftia phi . unFreerChurchT
    {-# INLINE hoistFreer #-}

deriving via ViaLiftLower FreerChurchT ins instance MonadTrans (FreerChurchT ins)

instance MonadTransFreer FreerChurchT where
    interpretMK f (FreerChurchT (HeftiaChurchT g)) = g $ f . unliftIns
    {-# INLINE interpretMK #-}

    reinterpretMK f = interpretMK f . hoistFreer liftLowerFT
    {-# INLINE reinterpretMK #-}