{-|
Module      : Control.Applicative.MultiExcept
Copyright   : (c) Owen Shepherd, 2021
License     : MIT
Maintainer  : owen@owen.cafe
Stability   : stable
Portability : portable
-}

{-# LANGUAGE ScopedTypeVariables #-}

module Control.Applicative.MultiExcept
  ( MultiExcept
  , fromEither
  , fromEitherPoly
  , join
  , runMultiExcept
  , succeed
  , throwError
  , throwErrors
  ) where

import Data.Bifunctor
import Data.Functor.Alt
import Data.DList.NonEmpty (NonEmptyDList)

-- | A 'MultiExcept' is a success value, or one or more errors.
data MultiExcept err a
  = Success a
  | Errors (NonEmptyDList err)
  deriving (MultiExcept err a -> MultiExcept err a -> Bool
(MultiExcept err a -> MultiExcept err a -> Bool)
-> (MultiExcept err a -> MultiExcept err a -> Bool)
-> Eq (MultiExcept err a)
forall a. (a -> a -> Bool) -> (a -> a -> Bool) -> Eq a
forall err a.
(Eq a, Eq err) =>
MultiExcept err a -> MultiExcept err a -> Bool
/= :: MultiExcept err a -> MultiExcept err a -> Bool
$c/= :: forall err a.
(Eq a, Eq err) =>
MultiExcept err a -> MultiExcept err a -> Bool
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MultiExcept err a -> MultiExcept err a -> Bool
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-> (MultiExcept err a -> MultiExcept err a -> Bool)
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MultiExcept err a -> MultiExcept err a -> Bool
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forall err a. (Ord a, Ord err) => Eq (MultiExcept err a)
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min :: MultiExcept err a -> MultiExcept err a -> MultiExcept err a
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MultiExcept err a -> MultiExcept err a -> Ordering
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Show)

-- | Run the computation.
runMultiExcept :: MultiExcept err a -> Either (NonEmptyDList err) a
runMultiExcept :: MultiExcept err a -> Either (NonEmptyDList err) a
runMultiExcept (Errors NonEmptyDList err
errs) = NonEmptyDList err -> Either (NonEmptyDList err) a
forall a b. a -> Either a b
Left NonEmptyDList err
errs
runMultiExcept (Success a
a) = a -> Either (NonEmptyDList err) a
forall a b. b -> Either a b
Right a
a

-- | Throw a single error.
throwError :: forall a err. err -> MultiExcept err a
throwError :: err -> MultiExcept err a
throwError = NonEmptyDList err -> MultiExcept err a
forall err a. NonEmptyDList err -> MultiExcept err a
Errors (NonEmptyDList err -> MultiExcept err a)
-> (err -> NonEmptyDList err) -> err -> MultiExcept err a
forall b c a. (b -> c) -> (a -> b) -> a -> c
. err -> NonEmptyDList err
forall (f :: * -> *) a. Applicative f => a -> f a
pure

-- | Throw one or more errors.
throwErrors :: forall a err. NonEmptyDList err -> MultiExcept err a
throwErrors :: NonEmptyDList err -> MultiExcept err a
throwErrors = NonEmptyDList err -> MultiExcept err a
forall err a. NonEmptyDList err -> MultiExcept err a
Errors

-- | Embeds a value into a 'MultiExcept' context.
succeed :: forall err a. a -> MultiExcept err a
succeed :: a -> MultiExcept err a
succeed = a -> MultiExcept err a
forall err a. a -> MultiExcept err a
Success

-- | Convert an 'Either' to a 'MultiExcept'.
fromEither :: Either err a -> MultiExcept err a
fromEither :: Either err a -> MultiExcept err a
fromEither (Left err
err) = err -> MultiExcept err a
forall a err. err -> MultiExcept err a
throwError err
err
fromEither (Right a
a) = a -> MultiExcept err a
forall err a. a -> MultiExcept err a
Success a
a

-- | Convert a multi-error 'Either' to a 'MultiExcept'.
fromEitherPoly :: Either (NonEmptyDList err) a -> MultiExcept err a
fromEitherPoly :: Either (NonEmptyDList err) a -> MultiExcept err a
fromEitherPoly (Left NonEmptyDList err
errs) = NonEmptyDList err -> MultiExcept err a
forall err a. NonEmptyDList err -> MultiExcept err a
Errors NonEmptyDList err
errs
fromEitherPoly (Right a
a) = a -> MultiExcept err a
forall err a. a -> MultiExcept err a
Success a
a

-- | Join nested 'MultiExcept's with the same error type.
--   Note that this doesn't imply a __useful__ 'Monad' instance.
--   The instance defined in terms of join discards errors on the RHS of '>>='.
join :: MultiExcept err (MultiExcept err a) -> MultiExcept err a
join :: MultiExcept err (MultiExcept err a) -> MultiExcept err a
join (Success MultiExcept err a
a) = MultiExcept err a
a
join (Errors NonEmptyDList err
a) = NonEmptyDList err -> MultiExcept err a
forall err a. NonEmptyDList err -> MultiExcept err a
Errors NonEmptyDList err
a

instance Functor (MultiExcept err) where
  fmap :: (a -> b) -> MultiExcept err a -> MultiExcept err b
fmap a -> b
f (Success a
a) = b -> MultiExcept err b
forall err a. a -> MultiExcept err a
Success (b -> MultiExcept err b) -> b -> MultiExcept err b
forall a b. (a -> b) -> a -> b
$ a -> b
f a
a
  fmap a -> b
_ (Errors NonEmptyDList err
errs) = NonEmptyDList err -> MultiExcept err b
forall err a. NonEmptyDList err -> MultiExcept err a
Errors NonEmptyDList err
errs

instance Bifunctor MultiExcept where
 bimap :: (a -> b) -> (c -> d) -> MultiExcept a c -> MultiExcept b d
bimap a -> b
_ c -> d
fa (Success c
a)    = d -> MultiExcept b d
forall err a. a -> MultiExcept err a
Success (d -> MultiExcept b d) -> d -> MultiExcept b d
forall a b. (a -> b) -> a -> b
$ c -> d
fa c
a
 bimap a -> b
ferr c -> d
_ (Errors NonEmptyDList a
err) = NonEmptyDList b -> MultiExcept b d
forall err a. NonEmptyDList err -> MultiExcept err a
Errors (NonEmptyDList b -> MultiExcept b d)
-> NonEmptyDList b -> MultiExcept b d
forall a b. (a -> b) -> a -> b
$ (a -> b) -> NonEmptyDList a -> NonEmptyDList b
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap a -> b
ferr NonEmptyDList a
err

instance Applicative (MultiExcept err) where
  pure :: a -> MultiExcept err a
pure = a -> MultiExcept err a
forall err a. a -> MultiExcept err a
Success

  Errors NonEmptyDList err
l <*> :: MultiExcept err (a -> b) -> MultiExcept err a -> MultiExcept err b
<*> Errors NonEmptyDList err
l' = NonEmptyDList err -> MultiExcept err b
forall err a. NonEmptyDList err -> MultiExcept err a
Errors (NonEmptyDList err -> MultiExcept err b)
-> NonEmptyDList err -> MultiExcept err b
forall a b. (a -> b) -> a -> b
$ NonEmptyDList err
l NonEmptyDList err -> NonEmptyDList err -> NonEmptyDList err
forall a. Semigroup a => a -> a -> a
<> NonEmptyDList err
l'
  Success a -> b
f <*> Success a
a = b -> MultiExcept err b
forall err a. a -> MultiExcept err a
Success (b -> MultiExcept err b) -> b -> MultiExcept err b
forall a b. (a -> b) -> a -> b
$ a -> b
f a
a
  Errors NonEmptyDList err
l <*> MultiExcept err a
_ = NonEmptyDList err -> MultiExcept err b
forall err a. NonEmptyDList err -> MultiExcept err a
Errors NonEmptyDList err
l
  MultiExcept err (a -> b)
_ <*> Errors NonEmptyDList err
l = NonEmptyDList err -> MultiExcept err b
forall err a. NonEmptyDList err -> MultiExcept err a
Errors NonEmptyDList err
l

instance Alt (MultiExcept err) where
  Success a
a <!> :: MultiExcept err a -> MultiExcept err a -> MultiExcept err a
<!> MultiExcept err a
_ = a -> MultiExcept err a
forall err a. a -> MultiExcept err a
Success a
a
  MultiExcept err a
_ <!> Success a
a = a -> MultiExcept err a
forall err a. a -> MultiExcept err a
Success a
a
  Errors NonEmptyDList err
l <!> Errors NonEmptyDList err
r = NonEmptyDList err -> MultiExcept err a
forall err a. NonEmptyDList err -> MultiExcept err a
Errors (NonEmptyDList err
l NonEmptyDList err -> NonEmptyDList err -> NonEmptyDList err
forall a. Semigroup a => a -> a -> a
<> NonEmptyDList err
r)

instance Foldable (MultiExcept err) where
  foldr :: (a -> b -> b) -> b -> MultiExcept err a -> b
foldr a -> b -> b
f b
acc (Success a
a) = a -> b -> b
f a
a b
acc
  foldr a -> b -> b
_ b
acc MultiExcept err a
_           = b
acc

instance Traversable (MultiExcept err) where
  traverse :: (a -> f b) -> MultiExcept err a -> f (MultiExcept err b)
traverse a -> f b
f (Success a
a)   = b -> MultiExcept err b
forall err a. a -> MultiExcept err a
Success (b -> MultiExcept err b) -> f b -> f (MultiExcept err b)
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
<$> a -> f b
f a
a
  traverse a -> f b
_ (Errors NonEmptyDList err
err) = MultiExcept err b -> f (MultiExcept err b)
forall (f :: * -> *) a. Applicative f => a -> f a
pure (MultiExcept err b -> f (MultiExcept err b))
-> MultiExcept err b -> f (MultiExcept err b)
forall a b. (a -> b) -> a -> b
$ NonEmptyDList err -> MultiExcept err b
forall err a. NonEmptyDList err -> MultiExcept err a
Errors NonEmptyDList err
err