65b6ea5 · text · git.iko.soy

git.iko.soy/text

Implement dropEnd

commit65b6ea51eacf2307e4a38e35b656c635e1e85648 authorBryan O'Sullivan <bos@serpentine.com> dateThu 6 Mar 2014, 20:07 (13 years ago) parent94e83cf

3 files changed+36−1

compare with master

unifiedsplit

Data/Text.hs+19−1 Data/Text/Unsafe.hs+11 tests/Tests/Properties.hs+6

Data/Text.hs+19−1

@@ -123,6 +123,7 @@ module Data.Text

123123 -- ** Breaking strings

124124 , take

125125 , drop

126+ , dropEnd

126127 , takeWhile

127128 , dropWhile

128129 , dropWhileEnd

@@ -214,7 +215,7 @@ import Data.Text.Internal.Private (span_)

214215import Data.Text.Internal (Text(..), empty, firstf, safe, text, textP)

215216import qualified Prelude as P

216217import Data.Text.Unsafe (Iter(..), iter, iter_, lengthWord16, reverseIter,

217− unsafeHead, unsafeTail)

218+ reverseIter_, unsafeHead, unsafeTail)

218219import Data.Text.Internal.Unsafe.Char (unsafeChr)

219220import qualified Data.Text.Internal.Functions as F

220221import qualified Data.Text.Internal.Encoding.Utf16 as U16

@@ -1038,6 +1039,23 @@ drop n t@(Text arr off len)

10381039 unstream (S.drop n (stream t)) = drop n t

10391040 #-}

10401041

1042+-- | /O(n)/ 'dropEnd' @n@ @t@ returns the prefix remaining after

1043+-- dropping @n@ characters from the end of @t@.

1044+--

1045+-- Examples:

1046+--

1047+-- > dropEnd 3 "foobar" == "foo"

1048+dropEnd :: Int -> Text -> Text

1049+dropEnd n t@(Text arr off len)

1050+ | n <= 0 = t

1051+ | n >= len = empty

1052+ | otherwise = loop (len-1) n

1053+ where loop i !m

1054+ | i <= 0 = empty

1055+ | m <= 1 = Text arr off i

1056+ | otherwise = loop (i+d) (m-1)

1057+ where d = reverseIter_ t i

1058+

10411059-- | /O(n)/ 'takeWhile', applied to a predicate @p@ and a 'Text',

10421060-- returns the longest prefix (possibly empty) of elements that

10431061-- satisfy @p@. Subject to fusion.

Data/Text/Unsafe.hs+11

@@ -18,6 +18,7 @@ module Data.Text.Unsafe

1818 , iter

1919 , iter_

2020 , reverseIter

21+ , reverseIter_

2122 , unsafeHead

2223 , unsafeTail

2324 , lengthWord16

@@ -94,6 +95,16 @@ reverseIter (Text arr off _len) i

9495 k = j - 1

9596{-# INLINE reverseIter #-}

9697

98+-- | /O(1)/ Iterate one step backwards through a UTF-16 array,

99+-- returning the delta to add (i.e. a negative number) to give the

100+-- next offset to iterate at.

101+reverseIter_ :: Text -> Int -> Int

102+reverseIter_ (Text arr off _len) i

103+ | m < 0xDC00 || m > 0xDFFF = -1

104+ | otherwise = -2

105+ where m = A.unsafeIndex arr (off+i)

106+{-# INLINE reverseIter_ #-}

107+

97108-- | /O(1)/ Return the length of a 'Text' in units of 'Word16'. This

98109-- is useful for sizing a target array appropriately before using

99110-- 'unsafeCopyToPtr'.

tests/Tests/Properties.hs+6

@@ -469,7 +469,11 @@ s_drop_s m = L.drop n `eqP` (unpackS . S.unstream . S.drop n)

469469sf_drop p n = (L.drop n . L.filter p) `eqP`

470470 (unpackS . S.drop n . S.filter p)

471471t_drop n = L.drop n `eqP` (unpackS . T.drop n)

472+t_dropEnd n = (L.reverse . L.drop n . L.reverse) `eqP`

473+ (unpackS . T.dropEnd n)

472474tl_drop n = L.drop n `eqP` (unpackS . TL.drop (fromIntegral n))

475+--tl_dropEnd n = (L.reverse . L.drop n . L.reverse) `eqP`

476+-- (unpackS . TL.dropEnd n)

473477s_take_drop m = (L.take n . L.drop n) `eqP` (unpackS . S.take n . S.drop n)

474478 where n = small m

475479s_take_drop_s m = (L.take n . L.drop n) `eqP`

@@ -1061,7 +1065,9 @@ tests =

10611065 testProperty "s_drop_s" s_drop_s,

10621066 testProperty "sf_drop" sf_drop,

10631067 testProperty "t_drop" t_drop,

1068+ testProperty "t_dropEnd" t_dropEnd,

10641069 testProperty "tl_drop" tl_drop,

1070+ -- testProperty "tl_dropEnd" tl_dropEnd,

10651071 testProperty "s_take_drop" s_take_drop,

10661072 testProperty "s_take_drop_s" s_take_drop_s,

10671073 testProperty "s_takeWhile" s_takeWhile,