65b6ea5 · text · git.iko.soy

git.iko.soy/text

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Implement dropEnd

65b6ea5Bryan O'Sullivan13 years ago

Data/Text.hs+19−1

compare with master

unifiedsplit

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

123 -- ** Breaking strings

124 , take

125 , drop

126+ , dropEnd

126 , takeWhile

127 , takeWhile

127 , dropWhile

128 , dropWhile

128 , dropWhileEnd

129 , dropWhileEnd

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

214import Data.Text.Internal (Text(..), empty, firstf, safe, text, textP)

215import Data.Text.Internal (Text(..), empty, firstf, safe, text, textP)

215import qualified Prelude as P

216import qualified Prelude as P

216import Data.Text.Unsafe (Iter(..), iter, iter_, lengthWord16, reverseIter,

217import Data.Text.Unsafe (Iter(..), iter, iter_, lengthWord16, reverseIter,

217− unsafeHead, unsafeTail)

218+ reverseIter_, unsafeHead, unsafeTail)

218import Data.Text.Internal.Unsafe.Char (unsafeChr)

219import Data.Text.Internal.Unsafe.Char (unsafeChr)

219import qualified Data.Text.Internal.Functions as F

220import qualified Data.Text.Internal.Functions as F

220import qualified Data.Text.Internal.Encoding.Utf16 as U16

221import qualified Data.Text.Internal.Encoding.Utf16 as U16

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

1038 unstream (S.drop n (stream t)) = drop n t

1039 unstream (S.drop n (stream t)) = drop n t

1039 #-}

1040 #-}

1040

1041

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+

1041-- | /O(n)/ 'takeWhile', applied to a predicate @p@ and a 'Text',

1059-- | /O(n)/ 'takeWhile', applied to a predicate @p@ and a 'Text',

1042-- returns the longest prefix (possibly empty) of elements that

1060-- returns the longest prefix (possibly empty) of elements that

1043-- satisfy @p@. Subject to fusion.

1061-- satisfy @p@. Subject to fusion.

Data/Text/Unsafe.hs+11

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

18 , iter

19 , iter_

20 , reverseIter

21+ , reverseIter_

21 , unsafeHead

22 , unsafeHead

22 , unsafeTail

23 , unsafeTail

23 , lengthWord16

24 , lengthWord16

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

94 k = j - 1

95 k = j - 1

95{-# INLINE reverseIter #-}

96{-# INLINE reverseIter #-}

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+

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

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

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

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

99-- 'unsafeCopyToPtr'.

110-- 'unsafeCopyToPtr'.

tests/Tests/Properties.hs+6

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

469sf_drop p n = (L.drop n . L.filter p) `eqP`

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

471t_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)

472tl_drop n = L.drop n `eqP` (unpackS . TL.drop (fromIntegral n))

474tl_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)

473s_take_drop m = (L.take n . L.drop n) `eqP` (unpackS . S.take n . S.drop n)

477s_take_drop m = (L.take n . L.drop n) `eqP` (unpackS . S.take n . S.drop n)

474 where n = small m

478 where n = small m

475s_take_drop_s m = (L.take n . L.drop n) `eqP`

479s_take_drop_s m = (L.take n . L.drop n) `eqP`

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

1061 testProperty "s_drop_s" s_drop_s,

1065 testProperty "s_drop_s" s_drop_s,

1062 testProperty "sf_drop" sf_drop,

1066 testProperty "sf_drop" sf_drop,

1063 testProperty "t_drop" t_drop,

1067 testProperty "t_drop" t_drop,

1068+ testProperty "t_dropEnd" t_dropEnd,

1064 testProperty "tl_drop" tl_drop,

1069 testProperty "tl_drop" tl_drop,

1070+ -- testProperty "tl_dropEnd" tl_dropEnd,

1065 testProperty "s_take_drop" s_take_drop,

1071 testProperty "s_take_drop" s_take_drop,

1066 testProperty "s_take_drop_s" s_take_drop_s,

1072 testProperty "s_take_drop_s" s_take_drop_s,

1067 testProperty "s_takeWhile" s_takeWhile,

1073 testProperty "s_takeWhile" s_takeWhile,