{-# LANGUAGE FlexibleInstances           #-}
{-# LANGUAGE GeneralizedNewtypeDeriving  #-}
{-# LANGUAGE MultiParamTypeClasses       #-}
{-# LANGUAGE UndecidableInstances        #-}

module Polysemy.ConstraintAbsorber.MonadState
  ( absorbState
  ) where

import           Polysemy
import           Polysemy.ConstraintAbsorber
import           Polysemy.State
import qualified Control.Monad.State.Class as S


------------------------------------------------------------------------------
-- | Introduce a local 'S.MonadState' constraint on 'Sem' --- allowing it to
-- interop nicely with MTL.
--
-- @since 0.3.0.0
absorbState
    :: Member (State s) r
    => (S.MonadState s (Sem r) => Sem r a)
       -- ^ A computation that requires an instance of 'S.MonadState' for
       -- 'Sem'. This might be something with type @'S.MonadState' s m => m a@.
    -> Sem r a
absorbState :: (MonadState s (Sem r) => Sem r a) -> Sem r a
absorbState = StateDict s (Sem r)
-> (forall s.
    Reifies s (StateDict s (Sem r)) :- MonadState s (Action (Sem r) s))
-> (MonadState s (Sem r) => Sem r a)
-> Sem r a
forall (p :: (* -> *) -> Constraint) (x :: (* -> *) -> * -> * -> *)
       d (r :: EffectRow) a.
d
-> (forall s. Reifies s d :- p (x (Sem r) s))
-> (p (Sem r) => Sem r a)
-> Sem r a
absorbWithSem @(S.MonadState _) @Action
  (Sem r s -> (s -> Sem r ()) -> StateDict s (Sem r)
forall s (m :: * -> *). m s -> (s -> m ()) -> StateDict s m
StateDict Sem r s
forall s (r :: EffectRow). Member (State s) r => Sem r s
get s -> Sem r ()
forall s (r :: EffectRow). Member (State s) r => s -> Sem r ()
put)
  ((Reifies s (StateDict s (Sem r)) =>
 Dict (MonadState s (Action (Sem r) s)))
-> Reifies s (StateDict s (Sem r))
   :- MonadState s (Action (Sem r) s)
forall (a :: Constraint) (b :: Constraint). (a => Dict b) -> a :- b
Sub Reifies s (StateDict s (Sem r)) =>
Dict (MonadState s (Action (Sem r) s))
forall (a :: Constraint). a => Dict a
Dict)
{-# INLINEABLE absorbState #-}


------------------------------------------------------------------------------
-- | A Dictionary of the functions we need to supply
-- to make an instance of State
data StateDict s m = StateDict
  { StateDict s m -> m s
get_ :: m s
  , StateDict s m -> s -> m ()
put_ :: s -> m ()
  }


------------------------------------------------------------------------------
-- | Wrapper for a monadic action with phantom type parameter for reflection.

-- Locally defined so that the instance we are going to build with reflection
-- must be coherent, that is there cannot be orphans.
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------------------------------------------------------------------------------
-- | Given a reifiable mtl State dictionary,
-- we can make an instance of @MonadState@ for the action
-- wrapped in @Action@.
instance ( Monad m
         , Reifies s' (StateDict s m)
         ) => S.MonadState s (Action m s') where
  get :: Action m s' s
get = m s -> Action m s' s
forall k k (m :: k -> *) (s' :: k) (a :: k). m a -> Action m s' a
Action (m s -> Action m s' s) -> m s -> Action m s' s
forall a b. (a -> b) -> a -> b
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forall s (m :: * -> *). StateDict s m -> m s
get_ (StateDict s m -> m s) -> StateDict s m -> m s
forall a b. (a -> b) -> a -> b
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  {-# INLINEABLE get #-}
  put :: s -> Action m s' ()
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  {-# INLINEABLE put #-}