{-# LANGUAGE FlexibleContexts #-}


-----------------------------------------------------------------------------

-- |

-- Module      :  Data.Tree.Lens

-- Copyright   :  (C) 2012-16 Edward Kmett

-- License     :  BSD-style (see the file LICENSE)

-- Maintainer  :  Edward Kmett <ekmett@gmail.com>

-- Stability   :  provisional

-- Portability :  MTPCs

--

----------------------------------------------------------------------------


module Data.Tree.Lens
  ( root
  , branches
  ) where

import Prelude ()

import Control.Lens.Internal.Prelude
import Control.Lens
import Data.Tree

-- $setup

-- >>> import Control.Lens

-- >>> import Data.Tree


-- | A 'Lens' that focuses on the root of a 'Tree'.

--

-- >>> view root $ Node 42 []

-- 42

root :: Lens' (Tree a) a
root :: forall a. Lens' (Tree a) a
root a -> f a
f (Node a
a [Tree a]
as) = (forall a. a -> [Tree a] -> Tree a
`Node` [Tree a]
as) forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
<$> a -> f a
f a
a
{-# INLINE root #-}

-- | A 'Lens' returning the direct descendants of the root of a 'Tree'

--

-- @'view' 'branches' ≡ 'subForest'@

branches :: Lens' (Tree a) [Tree a]
branches :: forall a. Lens' (Tree a) [Tree a]
branches [Tree a] -> f [Tree a]
f (Node a
a [Tree a]
as) = forall a. a -> [Tree a] -> Tree a
Node a
a forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
<$> [Tree a] -> f [Tree a]
f [Tree a]
as
{-# INLINE branches #-}