content: {-# LANGUAGE FlexibleInstances #-}
  {-# LANGUAGE FlexibleContexts #-}
  {-# LANGUAGE MultiParamTypeClasses #-}
  {-# LANGUAGE UndecidableInstances #-}
  {-# LANGUAGE GeneralizedNewtypeDeriving #-}
  {-# LANGUAGE TypeFamilies #-}
  {-# LANGUAGE DataKinds #-}
  module Control.Arrow.Transformer.Abstract.Failure(FailureT(..),runFailureT) where
  
  import Prelude hiding (id,(.),lookup,read)
  
  import Control.Category
  import Control.Arrow
  import Control.Arrow.Const
  import Control.Arrow.Environment as Env
  import Control.Arrow.Closure as Cls
  import Control.Arrow.Fail
  import Control.Arrow.Fix
  import Control.Arrow.Trans
  import Control.Arrow.Reader
  import Control.Arrow.State
  import Control.Arrow.Store as Store
  import Control.Arrow.Except as Exc
  import Control.Arrow.Order
  import Control.Arrow.Transformer.Kleisli
  import Control.Arrow.Fix.Context
  
  import Data.Abstract.Failure
  import Data.Abstract.Widening
  
  import Data.Profunctor
  import Data.Profunctor.Unsafe((.#))
  import Data.Coerce
  
  -- | Describes computations that can fail.
  newtype FailureT e c x y = FailureT (KleisliT (Failure e) c x y)
    deriving (Profunctor, Category, Arrow, ArrowChoice, ArrowLift, ArrowTrans, ArrowRun,
              ArrowConst r, ArrowState s, ArrowReader r,
              ArrowEnv var val, ArrowClosure expr cls, ArrowStore a b,
              ArrowExcept e', ArrowCallSite ctx)
  
  runFailureT :: FailureT e c x y -> c x (Failure e y)
  runFailureT = coerce
  {-# INLINE runFailureT #-}
  
  instance (ArrowChoice c, Profunctor c) => ArrowFail e (FailureT e c) where
    type Join x (FailureT e c) = ()
    fail = lift $ arr Fail
  
  instance (ArrowChoice c, ArrowApply c, Profunctor c) => ArrowApply (FailureT e c) where
    app = lift (app .# first coerce)
  
  instance (ArrowChoice c, ArrowFix (Underlying (FailureT e c) x y)) => ArrowFix (FailureT e c x y) where
    type Fix (FailureT e c x y) = Fix (Underlying (FailureT e c) x y)
  
  instance (ArrowChoice c, ArrowJoin c) => ArrowJoin (FailureT e c) where
    joinSecond lub f g = lift $ joinSecond (toJoin1 widening lub) (Success . f) (unlift g)
    {-# INLINE joinSecond #-}
  