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{-# LANGUAGE MultiParamTypeClasses #-} | |
{-# LANGUAGE FlexibleInstances #-} | |
{-# LANGUAGE FlexibleContexts #-} | |
{-# LANGUAGE TemplateHaskell #-} | |
{-# LANGUAGE TypeFamilies #-} | |
import Control.Lens | |
import Data.Maybe | |
import Data.Monoid | |
import Data.Tagged | |
data Constant a b = | |
Constant a | |
deriving (Eq, Show) | |
data Or a b = | |
Yes a | |
| No b | |
deriving (Eq, Show) | |
data These a b = | |
This a | |
| That b | |
| Both a b | |
deriving (Eq, Show) | |
data Possibly a b = | |
Impossible | |
| PossiblyA a | |
| PossiblyB b | |
deriving (Eq, Show) | |
class LeftLike p f k where | |
_LeftLike :: | |
Optic' p f (k a b) a | |
instance (Profunctor p, Functor f) => LeftLike p f Constant where | |
_LeftLike = | |
iso | |
(\(Constant a) -> a) | |
Constant | |
instance (Choice p, Applicative f) => LeftLike p f Or where | |
_LeftLike = | |
prism' | |
Yes | |
(\o -> case o of | |
Yes a -> Just a | |
No _ -> Nothing) | |
instance (Choice p, Applicative f) => LeftLike p f These where | |
_LeftLike = | |
prism' | |
This | |
(\t -> case t of | |
This a -> Just a | |
That _ -> Nothing | |
Both _ _ -> Nothing) | |
instance (Choice p, Applicative f) => LeftLike p f Either where | |
_LeftLike = | |
prism' | |
Left | |
(\e -> case e of | |
Left a -> Just a | |
Right _ -> Nothing) | |
instance (Choice p, Applicative f) => LeftLike p f Possibly where | |
_LeftLike = | |
prism' | |
PossiblyA | |
(\e -> case e of | |
PossiblyA a -> Just a | |
PossiblyB _ -> Nothing | |
Impossible -> Nothing) | |
getLeft :: | |
LeftLike (->) (Const (First a)) k => | |
a | |
-> k a b | |
-> a | |
getLeft a x = | |
fromMaybe a (x ^? _LeftLike) | |
data NEL a = | |
NEL a [a] | |
deriving (Eq, Show) | |
headNEL :: | |
Lens' (NEL a) a | |
headNEL = | |
lens | |
(\(NEL h _) -> h) | |
(\(NEL _ t) h -> NEL h t) | |
newtype ValidationNEL e a = | |
ValidationNEL (Either (NEL e) a) | |
deriving (Eq, Show) | |
makeWrapped ''ValidationNEL | |
instance (p ~ (->), Applicative f) => LeftLike p f ValidationNEL where | |
_LeftLike = | |
_Wrapped . _LeftLike . headNEL | |
putLeft :: | |
LeftLike Tagged Identity k => | |
a | |
-> k a b | |
putLeft = | |
(_LeftLike #) |
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