24 lines
697 B
Haskell
24 lines
697 B
Haskell
{-# LANGUAGE RankNTypes #-}
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module Control.Lens where
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import Control.Monad.Reader (MonadReader, asks)
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import Data.Functor.Const (Const (..))
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import Data.Functor.Identity (Identity (..))
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type Lens s t a b = forall f. Functor f => (a -> f b) -> s -> f t
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type Lens' s b = Lens s s b b
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lens :: (s -> a) -> (s -> b -> t) -> Lens s t a b
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lens sa sbt afb s = sbt s <$> afb (sa s)
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type Getting r s a = (a -> Const r a) -> s -> Const r s
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view :: MonadReader r m => Getting a r a -> m a
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view l = asks (getConst . l Const)
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type ASetter s t a b = (a -> Identity b) -> s -> Identity t
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set :: ASetter s t a b -> b -> s -> t
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set l b = runIdentity . l (\_ -> Identity b)
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