d581176 · text · git.iko.soy

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Implement and test lazy last

d581176Bryan O'Sullivan18 years ago

Data/Text/Lazy.hs+21−1

compare with master

unifiedsplit

@@ -45,7 +45,7 @@ module Data.Text.Lazy

45 , append

46 , uncons

47 , head

48− -- , last

48+ , last

49 -- , tail

50 -- , init

51 -- , null

@@ -151,6 +151,7 @@ import Prelude (Char, Bool(..), Functor(..), Int, Maybe(..), String,

151 Read(..), Show(..),

152 (&&), (||), (+), (-), (.), ($),

153 not, return, otherwise)

154+import qualified Prelude as P

154import Data.String (IsString(..))

155import Data.String (IsString(..))

155import qualified Data.Text as T

156import qualified Data.Text as T

156import qualified Data.Text.Fusion as S

157import qualified Data.Text.Fusion as S

@@ -250,6 +251,22 @@ head :: Text -> Char

250head t = S.head (stream t)

251head t = S.head (stream t)

251{-# INLINE head #-}

252{-# INLINE head #-}

252

253

254+-- | /O(1)/ Returns the last character of a 'Text', which must be

255+-- non-empty. Subject to array fusion.

256+last :: Text -> Char

257+last Empty = emptyError "last"

258+last (Chunk t ts) = go t ts

259+ where go _ (Chunk t' ts') = go t' ts'

260+ go t Empty = T.last t

261+{-# INLINE [1] last #-}

262+

263+{-# RULES

264+"LAZY TEXT last -> fused" [~1] forall t.

265+ last t = S.last (stream t)

266+"LAZY TEXT last -> unfused" [1] forall t.

267+ S.last (stream t) = last t

268+ #-}

269+

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

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

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

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

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

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

@@ -263,3 +280,6 @@ splitAt = loop

263 | otherwise = let (ts',ts'') = loop (n - len) ts

280 | otherwise = let (ts',ts'') = loop (n - len) ts

264 in (Chunk t ts', ts'')

281 in (Chunk t ts', ts'')

265 where len = T.length t

282 where len = T.length t

283+

284+emptyError :: String -> a

285+emptyError fun = P.error ("Data.Text.Lazy." ++ fun ++ ": empty input")

tests/Properties.hs+4−2

@@ -124,8 +124,9 @@ prop_TL_uncons s = uncons `eqP` (fmap (second unpackT) . TL.uncons)

124prop_S_head = head `eqEP` S.head

125prop_T_head = head `eqEP` T.head

126prop_TL_head = head `eqEP` TL.head

127+prop_S_last = last `eqEP` S.last

127prop_T_last = last `eqEP` T.last

128prop_T_last = last `eqEP` T.last

128−prop_T_lastS = last `eqEP` (S.last . S.stream)

129+prop_TL_last = last `eqEP` TL.last

129prop_T_tail = tail `eqEP` (unpackT . T.tail)

130prop_T_tail = tail `eqEP` (unpackT . T.tail)

130prop_T_tailS = tail `eqEP` (unpackT . S.unstream . S.tail . S.stream)

131prop_T_tailS = tail `eqEP` (unpackT . S.unstream . S.tail . S.stream)

131prop_T_init = init `eqEP` (unpackT . T.init)

132prop_T_init = init `eqEP` (unpackT . T.init)

@@ -300,8 +301,9 @@ tests = [

300 ("prop_S_head", mytest prop_S_head),

301 ("prop_S_head", mytest prop_S_head),

301 ("prop_T_head", mytest prop_T_head),

302 ("prop_T_head", mytest prop_T_head),

302 ("prop_TL_head", mytest prop_TL_head),

303 ("prop_TL_head", mytest prop_TL_head),

304+ ("prop_S_last", mytest prop_S_last),

303 ("prop_T_last", mytest prop_T_last),

305 ("prop_T_last", mytest prop_T_last),

304− ("prop_T_lastS", mytest prop_T_lastS),

306+ ("prop_TL_last", mytest prop_TL_last),

305 ("prop_T_tail", mytest prop_T_tail),

307 ("prop_T_tail", mytest prop_T_tail),

306 ("prop_T_tailS", mytest prop_T_tailS),

308 ("prop_T_tailS", mytest prop_T_tailS),

307 ("prop_T_init", mytest prop_T_init),

309 ("prop_T_init", mytest prop_T_init),