Add spanEnd and breakEnd to Data.Text

Author: TheMatten

src/Data/Text.hs

@@ -141,7 +141,9 @@ module Data.Text
     , breakOn
     , breakOnEnd
     , break
+    , breakEnd
     , span
+    , spanEnd
     , group
     , groupBy
     , inits
@@ -221,7 +223,7 @@ import qualified Data.Text.Internal.Fusion as S
 import qualified Data.Text.Internal.Fusion.Common as S
 import Data.Text.Encoding (decodeUtf8', encodeUtf8)
 import Data.Text.Internal.Fusion (stream, reverseStream, unstream)
-import Data.Text.Internal.Private (span_)
+import Data.Text.Internal.Private (span_, spanEnd_)
 import Data.Text.Internal (Text(..), empty, firstf, mul, safe, text)
 import Data.Text.Show (singleton, unpack, unpackCString#)
 import qualified Prelude as P
@@ -1333,6 +1335,15 @@ span p t = case span_ p t of
              (# hd,tl #) -> (hd,tl)
 {-# INLINE span #-}
 
+-- | /O(n)/ Similar to 'span', but searches from the end of the
+-- string.
+--
+-- >>> T.spanEnd (=='0') "AB000"
+-- ("AB", "000")
+spanEnd :: (Char -> Bool) -> Text -> (Text, Text)
+spanEnd p t = case spanEnd_ p t of (# hd, tl #) -> (hd, tl)
+{-# inline spanEnd #-}
+
 -- | /O(n)/ 'break' is like 'span', but the prefix returned is
 -- over elements that fail the predicate @p@.
 --
@@ -1342,6 +1353,15 @@ break :: (Char -> Bool) -> Text -> (Text, Text)
 break p = span (not . p)
 {-# INLINE break #-}
 
+-- | /O(n)/ Similar to 'break', but searches from the end of the
+-- string.
+--
+-- >>> T.breakEnd (=='0') "180cm"
+-- ("180","cm")
+breakEnd :: (Char -> Bool) -> Text -> (Text, Text)
+breakEnd p = spanEnd (not . p)
+{-# inline breakEnd #-}
+
 -- | /O(n)/ Group characters in a string according to a predicate.
 groupBy :: (Char -> Char -> Bool) -> Text -> [Text]
 groupBy p = loop

src/Data/Text/Internal/Private.hs

@@ -13,11 +13,12 @@ module Data.Text.Internal.Private
     (
       runText
     , span_
+    , spanEnd_
     ) where
 
 import Control.Monad.ST (ST, runST)
 import Data.Text.Internal (Text(..), text)
-import Data.Text.Unsafe (Iter(..), iter)
+import Data.Text.Unsafe (Iter(..), iter, reverseIter)
 import qualified Data.Text.Array as A
 
 span_ :: (Char -> Bool) -> Text -> (# Text, Text #)
@@ -30,6 +31,16 @@ span_ p t@(Text arr off len) = (# hd,tl #)
             where Iter c d       = iter t i
 {-# INLINE span_ #-}
 
+spanEnd_ :: (Char -> Bool) -> Text -> (# Text, Text #)
+spanEnd_ p t@(Text arr off len) = (# hd, tl #)
+  where hd = text arr off (k+1)
+        tl = text arr (off+k+1) (len-k-1)
+        !k = loop (len-1)
+        loop !i | i >= off && p c = loop (i+d)
+                | otherwise       = i
+         where (c, d)             = reverseIter t i
+{-# INLINE spanEnd_ #-}
+
 runText :: (forall s. (A.MArray s -> Int -> ST s Text) -> ST s Text) -> Text
 runText act = runST (act $ \ !marr !len -> do
                              arr <- A.unsafeFreeze marr