40a3168 · text · git.iko.soy

git.iko.soy/text

Add `unsnoc` to Data.Text and Data.Text.Lazy

Closes #171.

commit40a31689b03cbd3d181c6a9f95b9bac5a06ad56c authorBrian Chen <brian.chxn@gmail.com> dateTue 7 Mar 2017, 16:11 (10 years ago) parent831626d

3 files changed+32−1

compare with master

unifiedsplit

Data/Text.hs+12 Data/Text/Lazy.hs+10 tests/Tests/Properties.hs+10−1

Data/Text.hs+12

@@ -60,6 +60,7 @@ module Data.Text

6060 , snoc

6161 , append

6262 , uncons

63+ , unsnoc

6364 , head

6465 , last

6566 , tail

@@ -545,6 +546,17 @@ init (Text arr off len) | len <= 0 = emptyError "init"

545546 unstream (S.init (stream t)) = init t

546547 #-}

547548

549+-- | /O(1)/ Returns all but the last character and the last character of a

550+-- 'Text', or 'Nothing' if empty.

551+unsnoc :: Text -> Maybe (Text, Char)

552+unsnoc (Text arr off len)

553+ | len <= 0 = Nothing

554+ | n < 0xDC00 || n > 0xDFFF = Just (text arr off (len-1), unsafeChr n)

555+ | otherwise = Just (text arr off (len-2), U16.chr2 n0 n)

556+ where n = A.unsafeIndex arr (off+len-1)

557+ n0 = A.unsafeIndex arr (off+len-2)

558+{-# INLINE [1] unsnoc #-}

559+

548560-- | /O(1)/ Tests whether a 'Text' is empty or not. Subject to

549561-- fusion.

550562null :: Text -> Bool

Data/Text/Lazy.hs+10

@@ -68,6 +68,7 @@ module Data.Text.Lazy

6868 , snoc

6969 , append

7070 , uncons

71+ , unsnoc

7172 , head

7273 , last

7374 , tail

@@ -561,6 +562,15 @@ init Empty = emptyError "init"

561562 unstream (S.init (stream t)) = init t

562563 #-}

563564

565+-- | /O(n\/c)/ Returns the 'init' and 'last' of a 'Text', or 'Nothing' if

566+-- empty.

567+--

568+-- * It is no faster than using 'init' and 'last'.

569+unsnoc :: Text -> Maybe (Text, Char)

570+unsnoc Empty = Nothing

571+unsnoc ts@(Chunk _ _) = Just (init ts, last ts)

572+{-# INLINE unsnoc #-}

573+

564574-- | /O(1)/ Tests whether a 'Text' is empty or not. Subject to

565575-- fusion.

566576null :: Text -> Bool

tests/Tests/Properties.hs+10−1

@@ -9,7 +9,7 @@ module Tests.Properties

99 ) where

1010

1111import Control.Applicative ((<$>), (<*>))

12−import Control.Arrow ((***), second)

12+import Control.Arrow ((***), first, second)

1313import Data.Bits ((.&.))

1414import Data.Char (chr, isDigit, isHexDigit, isLower, isSpace, isLetter, isUpper, ord)

1515import Data.Int (Int8, Int16, Int32, Int64)

@@ -230,6 +230,13 @@ sf_uncons p = (uncons . L.filter p) `eqP`

230230 (fmap (second unpackS) . S.uncons . S.filter p)

231231t_uncons = uncons `eqP` (fmap (second unpackS) . T.uncons)

232232tl_uncons = uncons `eqP` (fmap (second unpackS) . TL.uncons)

233+

234+unsnoc xs@(_:_) = Just (init xs, last xs)

235+unsnoc [] = Nothing

236+

237+t_unsnoc = unsnoc `eqP` (fmap (first unpackS) . T.unsnoc)

238+tl_unsnoc = unsnoc `eqP` (fmap (first unpackS) . TL.unsnoc)

239+

233240s_head = head `eqP` S.head

234241sf_head p = (head . L.filter p) `eqP` (S.head . S.filter p)

235242t_head = head `eqP` T.head

@@ -976,6 +983,8 @@ tests =

976983 testProperty "sf_uncons" sf_uncons,

977984 testProperty "t_uncons" t_uncons,

978985 testProperty "tl_uncons" tl_uncons,

986+ testProperty "t_unsnoc" t_unsnoc,

987+ testProperty "tl_unsnoc" tl_unsnoc,

979988 testProperty "s_head" s_head,

980989 testProperty "sf_head" sf_head,

981990 testProperty "t_head" t_head,