{-# LANGUAGE GeneralizedNewtypeDeriving  #-}
{-# LANGUAGE TemplateHaskell             #-}

module Polysemy.ConstraintAbsorber.MonadRandom
  (
    absorbMonadRandom
  )
where

import           Polysemy
import           Polysemy.ConstraintAbsorber
import           Polysemy.RandomFu

import qualified Data.Random.Source            as R
import qualified Data.Random.Internal.Source   as R

------------------------------------------------------------------------------
-- | A dictionary of the functions we need to supply
-- to make an instance of MonadRandom
data RandomDict m = RandomDict { RandomDict m -> forall t. Prim t -> m t
getRandomPrim_ :: forall t. R.Prim t -> m t }

-- | 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.
newtype Action m s' a = Action { Action m s' a -> m a
action :: m a }
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-- | Given a reifiable mtl Error dictionary,
-- we can make an instance of @MonadRandom@ for the action
-- wrapped in @Action@.
$(R.monadRandom [d|
      instance ( Monad m
               , Reifies s' (RandomDict m)
               ) => R.MonadRandom (Action m s') where
          getRandomPrim t = Action
            $ getRandomPrim_ (reflect $ Proxy @s') t
          {-# INLINEABLE getRandomPrim #-}
  |])


-- | absorb a @MonadError e@ constraint into @Member (Error e) r => Sem r@
absorbMonadRandom :: forall r a. (Member RandomFu r)
  => (R.MonadRandom (Sem r) => Sem r a)
  -> Sem r a
absorbMonadRandom :: (MonadRandom (Sem r) => Sem r a) -> Sem r a
absorbMonadRandom = RandomDict (Sem r)
-> (forall s.
    Reifies s (RandomDict (Sem r)) :- MonadRandom (Action (Sem r) s))
-> (MonadRandom (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 @R.MonadRandom @Action
  ((forall t. Prim t -> Sem r t) -> RandomDict (Sem r)
forall (m :: * -> *). (forall t. Prim t -> m t) -> RandomDict m
RandomDict (forall (r :: EffectRow) t.
MemberWithError RandomFu r =>
Prim t -> Sem r t
forall t. MemberWithError RandomFu r => Prim t -> Sem r t
getRandomPrim @r))
  ((Reifies s (RandomDict (Sem r)) =>
 Dict (MonadRandom (Action (Sem r) s)))
-> Reifies s (RandomDict (Sem r)) :- MonadRandom (Action (Sem r) s)
forall (a :: Constraint) (b :: Constraint). (a => Dict b) -> a :- b
Sub Reifies s (RandomDict (Sem r)) =>
Dict (MonadRandom (Action (Sem r) s))
forall (a :: Constraint). a => Dict a
Dict)
{-# INLINEABLE absorbMonadRandom #-}