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mbrcknl/LensRef.hs

Created October 9, 2014 02:05
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LensRef.hs
{-# LANGUAGE Rank2Types #-}
type Lens s t a b = forall f. Functor f => (a -> f b) -> (s -> f t)
type Ref s t a b = s -> Rep a b t
data Rep a b t = Rep a (b -> t)
instance Functor (Rep a b) where
fmap f (Rep a g) = Rep a (f . g)
lens2Ref :: Lens s t a b -> Ref s t a b
lens2Ref r = r (\b -> Rep b id)
ref2Lens :: Ref s t a b -> Lens s t a b
ref2Lens l k x = case l x of
Rep s f -> fmap f (k s)
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