Extras.hs

-- This file is part of hs-concise
-- Copyright (C) 2016  Fraser Tweedale
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{-# LANGUAGE NoImplicitPrelude #-}

module Control.Lens.Cons.Extras
  (
    recons
  , unfoldr
  ) where

import Data.Function (id)
import Data.Maybe (Maybe)
import Data.String (String)
import Data.Word (Word8)

import Control.Lens
import Control.Lens ((#))
import Control.Lens.Cons (Cons, cons, uncons)
import Control.Lens.Empty (AsEmpty(..))
import Control.Lens.Fold (foldrOf, unfolded)

import Control.Lens.Iso (lazy, strict)
import qualified Data.ByteString as B
import qualified Data.ByteString.Lazy as L
import Data.ByteString.Lens (packedBytes, unpackedBytes)
import qualified Data.Text as T
import Data.Text.Lens (packed, unpacked)
import qualified Data.Text.Lazy as TL

-- | Convert one type with a 'Cons' instance into the other.
--
-- Rewrite rules are provided for efficient conversion between
-- 'String' and 'Text', @['Word8']@ and 'ByteString', and lazy and
-- strict 'Text' and 'ByteString'.  Programs must be compiled
-- with @-O@ to use them.
--
-- Although the type does not prove it, if @(recons . recons)@
-- exists it should obey:
--
-- > recons . recons ≡ id
--
{-# NOINLINE [2] recons #-}
recons :: (Cons s1 s1 a a, Cons s2 s2 a a, AsEmpty s2) => Getter s1 s2
recons = to (unfoldr uncons)

-- | > unfoldr f = foldrOf (unfolded f) cons (_Empty # ())
--
unfoldr :: (Cons s2 s2 a a, AsEmpty s2) => (s1 -> Maybe (a, s1)) -> s1 -> s2
unfoldr f = foldrOf (unfolded f) cons (_Empty # ())

{-# RULES
"recons/id"
  recons = id
"recons/string-text"
  recons = packed :: Getter String T.Text
"recons/text-string"
  recons = unpacked :: Getter T.Text String
"recons/string-lazytext"
  recons = packed :: Getter String TL.Text
"recons/lazytext-string"
  recons = unpacked :: Getter TL.Text String
"recons/text-strict"
  recons = strict :: Getter TL.Text T.Text
"recons/text-lazy"
  recons = lazy :: Getter T.Text TL.Text
"recons/list-bs"
  recons = packedBytes :: Getter [Word8] B.ByteString
"recons/bs-list"
  recons = unpackedBytes :: Getter B.ByteString [Word8]
"recons/list-lazybs"
  recons = packedBytes :: Getter [Word8] L.ByteString
"recons/lazybs-list"
  recons = unpackedBytes :: Getter L.ByteString [Word8]
"recons/bs-strict"
  recons = strict :: Getter L.ByteString B.ByteString
"recons/bs-lazy"
  recons = lazy :: Getter B.ByteString L.ByteString
 #-}