b15c35e · text · git.iko.soy

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Implement and test lazy takeWhile and dropWhile

b15c35eBryan O'Sullivan18 years ago

Data/Text/Lazy.hs+40−2

compare with master

unifiedsplit

@@ -96,8 +96,8 @@ module Data.Text.Lazy

96 -- ** Breaking strings

97 , take

98 , drop

99− -- , takeWhile

99+ , takeWhile

100− -- , dropWhile

100+ , dropWhile

101 , splitAt

102 -- , span

103 -- , break

@@ -536,6 +536,44 @@ drop i t0

536 unstream (S.drop n (stream t)) = drop n t

537 #-}

538

539+-- | /O(n)/ 'takeWhile', applied to a predicate @p@ and a 'Text', returns

540+-- the longest prefix (possibly empty) of elements that satisfy @p@.

541+-- This function is subject to array fusion.

542+takeWhile :: (Char -> Bool) -> Text -> Text

543+takeWhile p t0 = takeWhile' t0

544+ where takeWhile' Empty = Empty

545+ takeWhile' (Chunk t ts) =

546+ case T.findIndex (not . p) t of

547+ Just n | n > 0 -> Chunk (T.take n t) Empty

548+ | otherwise -> Empty

549+ Nothing -> Chunk t (takeWhile' ts)

550+{-# INLINE [1] takeWhile #-}

551+

552+{-# RULES

553+"LAZY TEXT takeWhile -> fused" [~1] forall p t.

554+ takeWhile p t = unstream (S.takeWhile p (stream t))

555+"LAZY TEXT takeWhile -> unfused" [1] forall p t.

556+ unstream (S.takeWhile p (stream t)) = takeWhile p t

557+ #-}

558+

559+-- | /O(n)/ 'dropWhile' @p@ @xs@ returns the suffix remaining after

560+-- 'takeWhile' @p@ @xs@. This function is subject to array fusion.

561+dropWhile :: (Char -> Bool) -> Text -> Text

562+dropWhile p t0 = dropWhile' t0

563+ where dropWhile' Empty = Empty

564+ dropWhile' (Chunk t ts) =

565+ case T.findIndex (not . p) t of

566+ Just n -> Chunk (T.drop n t) ts

567+ Nothing -> dropWhile' ts

568+{-# INLINE [1] dropWhile #-}

569+

570+{-# RULES

571+"LAZY TEXT dropWhile -> fused" [~1] forall p t.

572+ dropWhile p t = unstream (S.dropWhile p (stream t))

573+"LAZY TEXT dropWhile -> unfused" [1] forall p t.

574+ unstream (S.dropWhile p (stream t)) = dropWhile p t

575+ #-}

576+

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

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

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

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

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

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

tests/Properties.hs+8−4

@@ -221,10 +221,12 @@ prop_TL_take n = L.take n `eqP` (unpackT . TL.take (fromIntegral n)

221prop_S_drop n = L.drop n `eqP` (unpackT . S.drop n)

222prop_T_drop n = L.drop n `eqP` (unpackT . T.drop n)

223prop_TL_drop n = L.drop n `eqP` (unpackT . TL.drop n)

224+prop_S_takeWhile p = L.takeWhile p `eqP` (unpackT . S.takeWhile p)

224prop_T_takeWhile p = L.takeWhile p `eqP` (unpackT . T.takeWhile p)

225prop_T_takeWhile p = L.takeWhile p `eqP` (unpackT . T.takeWhile p)

225−prop_T_takeWhileS p = L.takeWhile p `eqP` (unpackT . S.unstream . S.takeWhile p . S.stream)

226+prop_TL_takeWhile p = L.takeWhile p `eqP` (unpackT . TL.takeWhile p)

227+prop_S_dropWhile p = L.dropWhile p `eqP` (unpackT . S.dropWhile p)

226prop_T_dropWhile p = L.dropWhile p `eqP` (unpackT . T.dropWhile p)

228prop_T_dropWhile p = L.dropWhile p `eqP` (unpackT . T.dropWhile p)

227−prop_T_dropWhileS p = L.dropWhile p `eqP` (unpackT . S.unstream . S.dropWhile p . S.stream)

229+prop_TL_dropWhile p = L.dropWhile p `eqP` (unpackT . S.dropWhile p)

228prop_T_splitAt n = L.splitAt n `eqP` (unpack2 . T.splitAt n)

230prop_T_splitAt n = L.splitAt n `eqP` (unpack2 . T.splitAt n)

229prop_TL_splitAt n = L.splitAt n `eqP` (unpack2 . TL.splitAt n)

231prop_TL_splitAt n = L.splitAt n `eqP` (unpack2 . TL.splitAt n)

230prop_T_span p = L.span p `eqP` (unpack2 . T.span p)

232prop_T_span p = L.span p `eqP` (unpack2 . T.span p)

@@ -418,10 +420,12 @@ tests = [

418 ("prop_S_drop", mytest prop_S_drop),

420 ("prop_S_drop", mytest prop_S_drop),

419 ("prop_T_drop", mytest prop_T_drop),

421 ("prop_T_drop", mytest prop_T_drop),

420 ("prop_TL_drop", mytest prop_TL_drop),

422 ("prop_TL_drop", mytest prop_TL_drop),

423+ ("prop_S_takeWhile", mytest prop_S_takeWhile),

421 ("prop_T_takeWhile", mytest prop_T_takeWhile),

424 ("prop_T_takeWhile", mytest prop_T_takeWhile),

422− ("prop_T_takeWhileS", mytest prop_T_takeWhileS),

425+ ("prop_TL_takeWhile", mytest prop_TL_takeWhile),

426+ ("prop_S_dropWhile", mytest prop_S_dropWhile),

423 ("prop_T_dropWhile", mytest prop_T_dropWhile),

427 ("prop_T_dropWhile", mytest prop_T_dropWhile),

424− ("prop_T_dropWhileS", mytest prop_T_dropWhileS),

428+ ("prop_TL_dropWhile", mytest prop_TL_dropWhile),

425 ("prop_T_splitAt", mytest prop_T_splitAt),

429 ("prop_T_splitAt", mytest prop_T_splitAt),

426 ("prop_T_span", mytest prop_T_span),

430 ("prop_T_span", mytest prop_T_span),

427 ("prop_T_break", mytest prop_T_break),

431 ("prop_T_break", mytest prop_T_break),