a74d560 · text · git.iko.soy

git.iko.soy/text

Implement uncons

--HG-- extra : convert_revision : a4c61ea8be58b75e94f170a0c1d687e6f899c5ab

commita74d560022bb2e7bb4f47ed6a41d557d8b06fdbc authorBryan O'Sullivan <bos@serpentine.com> dateTue 27 Jan 2009, 06:43 (18 years ago) parenta70e3a0

2 files changed+24−2

compare with master

unifiedsplit

Data/Text.hs+10−1 Data/Text/Fusion.hs+14−1

Data/Text.hs+10−1

@@ -40,6 +40,7 @@ module Data.Text

4040 , cons

4141 , snoc

4242 , append

43+ , uncons

4344 , head

4445 , last

4546 , tail

@@ -97,7 +98,7 @@ module Data.Text

9798 , zipWith

9899 ) where

99100

100−import Prelude (Char, Bool, Int, Maybe, String,

101+import Prelude (Char, Bool, Int, Maybe(..), String,

101102 Eq, (==), (++), error,

102103 Show, showsPrec,

103104 Read, readsPrec,

@@ -227,6 +228,14 @@ head :: Text -> Char

227228head t = S.head (stream t)

228229{-# INLINE head #-}

229230

231+-- | /O(1)/ Returns the first character and rest of a 'Text', or

232+-- 'Nothing' if empty. Subject to array fusion.

233+uncons :: Text -> Maybe (Char, Text)

234+uncons t = case S.uncons (stream t) of

235+ Just (c, s) -> Just (c, unstream s)

236+ Nothing -> Nothing

237+{-# INLINE uncons #-}

238+

230239-- | /O(n)/ Returns the last character of a 'Text', which must be

231240-- non-empty. Subject to array fusion.

232241last :: Text -> Char

Data/Text/Fusion.hs+14−1

@@ -28,6 +28,7 @@ module Data.Text.Fusion

2828 , cons

2929 , snoc

3030 , append

31+ , uncons

3132 , head

3233 , tail

3334 , last

@@ -241,7 +242,19 @@ head (Stream next s0 _len) = loop_head s0

241242 Done -> error "head: Empty list"

242243{-# INLINE [0] head #-}

243244

244−-- | /O(n)/ Returns the last character of a Stream Char, which must be non-empty.

245+-- | /O(1)/ Returns the first character and remainder of a 'Stream

246+-- Char', or 'Nothing' if empty. Subject to array fusion.

247+uncons :: Stream Char -> Maybe (Char, Stream Char)

248+uncons (Stream next s0 len) = loop_uncons s0

249+ where

250+ loop_uncons !s = case next s of

251+ Yield x s1 -> Just (x, Stream next s1 (len-1))

252+ Skip s' -> loop_uncons s'

253+ Done -> Nothing

254+{-# INLINE [0] uncons #-}

255+

256+-- | /O(n)/ Returns the last character of a 'Stream Char', which must

257+-- be non-empty.

245258last :: Stream Char -> Char

246259last (Stream next s0 _len) = loop0_last s0

247260 where