37ab912 · text · git.iko.soy

git.iko.soy/text

Implement and test lazy uncons

--HG-- extra : convert_revision : 716cea953f67af09149fd65de5f55b30cb2660c0

commit37ab912d99670f729d99c7901ea29c3843a6d583 authorBryan O'Sullivan <bos@serpentine.com> dateSun 1 Mar 2009, 06:50 (18 years ago) parentea7cc8a

2 files changed+19−4

compare with master

unifiedsplit

Data/Text/Lazy.hs+11−1 tests/Properties.hs+8−3

Data/Text/Lazy.hs+11−1

@@ -43,7 +43,7 @@ module Data.Text.Lazy

4343 , cons

4444 , snoc

4545 , append

46− -- , uncons

46+ , uncons

4747 -- , head

4848 -- , last

4949 -- , tail

@@ -155,6 +155,7 @@ import Data.String (IsString(..))

155155import qualified Data.Text as T

156156import qualified Data.Text.Fusion as S

157157import qualified Data.Text.Fusion.Internal as S

158+import qualified Data.Text.Unsafe as T

158159import Data.Text.Lazy.Fusion

159160import Data.Text.Lazy.Internal

160161

@@ -233,6 +234,15 @@ append xs ys = foldrChunks Chunk ys xs

233234 unstream (S.append (stream t1) (stream t2)) = append t1 t2

234235 #-}

235236

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

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

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

240+uncons Empty = Nothing

241+uncons (Chunk t ts) =

242+ Just (T.unsafeHead t,

243+ if T.length t == 1 then ts else Chunk (T.unsafeTail t) ts)

244+{-# INLINE uncons #-}

245+

236246-- | /O(n)/ 'splitAt' @n t@ returns a pair whose first element is a

237247-- prefix of @t@ of length @n@, and whose second is the remainder of

238248-- the string. It is equivalent to @('take' n t, 'drop' n t)@.

tests/Properties.hs+8−3

@@ -113,10 +113,14 @@ prop_T_snoc x = (++ [x]) `eqP` (unpackT . (flip T.snoc) x)

113113prop_TL_snoc x = (++ [x]) `eqP` (unpackT . (flip TL.snoc) x)

114114prop_T_append s = (s++) `eqP` (unpackT . T.append (T.pack s))

115115prop_T_appendS s = (s++) `eqP` (unpackT . S.unstream . S.append (S.stream (T.pack s)) . S.stream)

116+

117+uncons (x:xs) = Just (x,xs)

118+uncons _ = Nothing

119+

116120prop_T_uncons s = uncons `eqP` (fmap (second unpackT) . T.uncons)

117− where uncons (x:xs) = Just (x,xs)

118− uncons _ = Nothing

119− types = s :: String

121+ where types = s :: String

122+prop_TL_uncons s = uncons `eqP` (fmap (second unpackT) . TL.uncons)

123+ where types = s :: String

120124prop_T_head = head `eqEP` T.head

121125prop_T_last = last `eqEP` T.last

122126prop_T_lastS = last `eqEP` (S.last . S.stream)

@@ -290,6 +294,7 @@ tests = [

290294 ("prop_T_append", mytest prop_T_append),

291295 ("prop_T_appendS", mytest prop_T_appendS),

292296 ("prop_T_uncons", mytest prop_T_uncons),

297+ ("prop_TL_uncons", mytest prop_TL_uncons),

293298 ("prop_T_head", mytest prop_T_head),

294299 ("prop_T_last", mytest prop_T_last),

295300 ("prop_T_lastS", mytest prop_T_lastS),