SingLens.hs

{-# LANGUAGE TemplateHaskell, TypeSynonymInstances, FlexibleInstances, MultiParamTypeClasses, UndecidableInstances #-}
module SingLens where

import Control.Lens
import SuperLens ((???), makeLensesPlus)

data Foo = Foo { _bar :: String, _baz :: Int } deriving Show
makeLensesPlus ''Foo

-- | f
-- >>> f
-- Foo {_bar = "four", _baz = 3}
f :: Foo
f = Foo "four" 3

-- | g
-- >>> g
-- "four"
g :: String
g = view (???) f

-- | h
-- >>> h
-- 3
h :: Int
h = view (???) f

-- | i
-- >>> i
-- Foo {_bar = "bar", _baz = 3}
i :: Foo
i = set (???) "bar" f