Biplate2.hs

{-# LANGUAGE DeriveDataTypeable #-}
{-# LANGUAGE TypeApplications   #-}

module Biplate where

import Control.Lens
import Data.Data
import Data.Data.Lens

data B = C | D | E
  deriving (Data, Enum, Show)

newtype X = X B
  deriving (Data, Show)

newtype Y = Y B
  deriving (Data, Show)

data Foo = N | I | Bar X | Baz Y
  deriving (Data, Show)

n :: Foo
n = N

i :: Foo
i = I

bar :: Foo
bar = Bar (X C)

baz :: Foo
baz = Baz (Y D)

n' :: Foo
n' = n & (biplate :: Traversal' Foo B) %~ succ

i' :: Foo
i' = i & biplate %~ (succ :: B -> B)

bar' :: Foo
bar' = bar & biplate %~ (succ :: B -> B)

baz' :: Foo
baz' = baz & biplate %~ succ @B

-- λ> (n, i, bar, baz)
-- (N,I,Bar (X C),Baz (Y D))
-- λ> (n', i', bar', baz')
-- (N,I,Bar (X D),Baz (Y E))