BiplateExample.hs

{-# LANGUAGE DeriveDataTypeable #-}

module Biplate where

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

newtype X a = X a
  deriving (Data, Show)

newtype Y a = Y a
  deriving (Data, Show)

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

n :: Foo Int
n = N

i :: Foo Int
i = I

bar :: Foo Int
bar = Bar (X 5)

baz :: Foo Int
baz = Baz (Y 10)

n' :: Foo Int
n' = n & (biplate :: Traversal' (Foo Int) Int) *~ 2

i' :: Foo Int
i' = i & biplate *~ (2 :: Int)

bar' :: Foo Int
bar' = bar & biplate *~ (2 :: Int)

baz' :: Foo Int
baz' = baz & biplate *~ (2 :: Int)

-- λ> (n, i, bar, baz)
-- (N,I,Bar (X 5),Baz (Y 10))
-- λ> (n', i', bar', baz')
-- (N,I,Bar (X 10),Baz (Y 20))