Lens.hs

{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE PatternSynonyms #-}
{-# LANGUAGE ViewPatterns #-}
-----------------------------------------------------------------------------
-- |
-- Module      :  Data.Text.Lazy.Lens
-- Copyright   :  (C) 2012-2016 Edward Kmett
-- License     :  BSD-style (see the file LICENSE)
-- Maintainer  :  Edward Kmett <ekmett@gmail.com>
-- Stability   :  experimental
-- Portability :  non-portable
--
----------------------------------------------------------------------------
module Data.Text.Lazy.Lens
  ( packed, unpacked
  , _Text
  , text
  , builder
  , utf8
  , pattern Text
  ) where

import Control.Lens.Type
import Control.Lens.Getter
import Control.Lens.Fold
import Control.Lens.Iso
import Control.Lens.Prism
import Control.Lens.Review
import Control.Lens.Setter
import Control.Lens.Traversal
import Data.ByteString.Lazy (ByteString)
import Data.Monoid
import Data.Text.Lazy (Text)
import qualified Data.Text.Lazy as Text
import qualified Data.Text.Lazy.Builder as Builder
import Data.Text.Lazy.Builder (Builder)
import Data.Text.Lazy.Encoding

-- $setup
-- >>> :set -XOverloadedStrings
-- >>> import Control.Lens
-- >>> import qualified Data.ByteString.Lazy as ByteString

-- | This isomorphism can be used to 'pack' (or 'unpack') lazy 'Text'.
--
-- >>> "hello"^.packed -- :: Text
-- "hello"
--
-- @
-- 'pack' x ≡ x '^.' 'packed'
-- 'unpack' x ≡ x '^.' 'from' 'packed'
-- 'packed' ≡ 'from' 'unpacked'
-- @
packed :: Iso' String Text
packed = iso Text.pack Text.unpack
{-# INLINE packed #-}

-- | This isomorphism can be used to 'unpack' (or 'pack') lazy 'Text'.
--
-- >>> "hello"^.unpacked -- :: String
-- "hello"
--
-- @
-- 'pack' x ≡ x '^.' 'from' 'unpacked'
-- 'unpack' x ≡ x '^.' 'packed'
-- @
--
-- This 'Iso' is provided for notational convenience rather than out of great need, since
--
-- @
-- 'unpacked' ≡ 'from' 'packed'
-- @
unpacked :: Iso' Text String
unpacked = iso Text.unpack Text.pack
{-# INLINE unpacked #-}

-- | This is an alias for 'unpacked' that makes it clearer how to use it with @('#')@.
--
-- @
-- '_Text' = 'from' 'packed'
-- @
--
-- >>> _Text # "hello" -- :: Text
-- "hello"
_Text :: Iso' Text String
_Text = from packed
{-# INLINE _Text #-}

-- | Convert between lazy 'Text' and 'Builder' .
--
-- @
-- 'fromLazyText' x ≡ x '^.' 'builder'
-- 'toLazyText' x ≡ x '^.' 'from' 'builder'
-- @
builder :: Iso' Text Builder
builder = iso Builder.fromLazyText Builder.toLazyText
{-# INLINE builder #-}

-- | Traverse the individual characters in a 'Text'.
--
-- >>> anyOf text (=='c') "chello"
-- True
--
-- @
-- 'text' = 'unpacked' . 'traversed'
-- @
--
-- When the type is unambiguous, you can also use the more general 'each'.
--
-- @
-- 'text' ≡ 'each'
-- @
--
-- Note that when just using this as a 'Setter', @'setting' 'Data.Text.Lazy.map'@
-- can be more efficient.
text :: IndexedTraversal' Int Text Char
text = unpacked . traversed
{-# INLINE [0] text #-}

{-# RULES
"lazy text -> map"    text = sets Text.map        :: ASetter' Text Char;
"lazy text -> imap"   text = isets imapLazy       :: AnIndexedSetter' Int Text Char;
"lazy text -> foldr"  text = foldring Text.foldr  :: Getting (Endo r) Text Char;
"lazy text -> ifoldr" text = ifoldring ifoldrLazy :: IndexedGetting Int (Endo r) Text Char;
 #-}

imapLazy :: (Int -> Char -> Char) -> Text -> Text
imapLazy f = snd . Text.mapAccumL (\i a -> i `seq` (i + 1, f i a)) 0
{-# INLINE imapLazy #-}

ifoldrLazy :: (Int -> Char -> a -> a) -> a -> Text -> a
ifoldrLazy f z xs = Text.foldr (\ x g i -> i `seq` f i x (g (i+1))) (const z) xs 0
{-# INLINE ifoldrLazy #-}

-- | Encode\/Decode a lazy 'Text' to\/from lazy 'ByteString', via UTF-8.
--
-- Note: This function does not decode lazily, as it must consume the entire
-- input before deciding whether or not it fails.
--
-- >>> ByteString.unpack (utf8 # "☃")
-- [226,152,131]
utf8 :: Prism' ByteString Text
utf8 = prism' encodeUtf8 (preview _Right . decodeUtf8')
{-# INLINE utf8 #-}

pattern Text :: String -> Text
pattern Text a <- (view _Text -> a) where
  Text a = review _Text a