{-# LANGUAGE RankNTypes #-}
module Ahc.Data.Lens where

import Control.Applicative

import Data.Functor.Identity

type Lens s t a b = forall f. Functor f => (a -> f b) -> s -> f t

type Lens' s a = Lens s s a a

get :: Lens s t a b -> s -> a
get l = getConst . l Const

over :: Lens s t a b -> (a -> b) -> s -> t
over l m = runIdentity . l (Identity . m)

set :: Lens s t a b -> b -> s -> t
set l b a = over l (const b) a

(.~) :: Lens s t a b -> b -> s -> t
(.~) = set
infixr 4 .~

(%~) :: Lens s t a b -> (a -> b) -> s -> t
(%~) = over
infixr 4 %~

(^.) :: s -> Lens s t a b -> a
x ^. l = get l x

(&) :: t1 -> (t1 -> t2) -> t2
x & f = f x
infixr 0 &

lens :: (s -> a) -> (s -> b -> t) -> Lens s t a b
lens sa sbt afb s = sbt s <$> afb (sa s)