implement dropAround

IaFP · Jan 22, 2018 · f0708ba · f0708ba
1 parent a44695d
commit f0708ba
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Showing 3 changed files with 30 additions and 3 deletions.
diff --git a/src-test/Tests.hs b/src-test/Tests.hs
@@ -78,6 +78,7 @@ qcProps = testGroup "Properties"
   , QC.testProperty "reverse"     $ \t -> IUT.reverse (IUT.fromText t) == IUT.fromText (T.reverse t)
   , QC.testProperty "filter"      $ \p t -> IUT.filter p (IUT.fromText t) == IUT.fromText (T.filter p t)
   , QC.testProperty "replicate"   $ \n t -> IUT.replicate n (IUT.fromText t) == IUT.fromText (T.replicate n t)
+  , QC.testProperty "dropAround"  $ \p t -> IUT.dropAround p (IUT.fromText t) == IUT.fromText (T.dropAround p t)
 
   , QC.testProperty "splitAtEnd" $ \t ->
       let t' = IUT.fromText t

diff --git a/src/Data/Text/Short.hs b/src/Data/Text/Short.hs
@@ -66,6 +66,8 @@ module Data.Text.Short
     , dropWhile
     , dropWhileEnd
 
+    , dropAround
+
       -- ** Pair-valued functions
     , splitAt
     , splitAtEnd

diff --git a/src/Data/Text/Short/Internal.hs b/src/Data/Text/Short/Internal.hs
@@ -52,9 +52,11 @@ module Data.Text.Short.Internal
     , intersperse
     , intercalate
     , reverse
-    , filter
     , replicate
 
+    , filter
+    , dropAround
+
       -- * Conversions
       -- ** 'Char'
     , singleton
@@ -947,8 +949,8 @@ filter p t
         t1sz <- go mba ofs2 ofs1
         return t1sz
   where
-    mofs1 = findOfs (not . p) t 0 -- first non-accepted Char
-    mofs2 = findOfs p t (fromMaybe 0 mofs1) -- first accepted Char
+    mofs1 = findOfs (not . p) t (B 0) -- first non-accepted Char
+    mofs2 = findOfs p t (fromMaybe (B 0) mofs1) -- first accepted Char
 
     t0sz = toB t
 
@@ -962,6 +964,28 @@ filter p t
                             go mba (t0ofs+cpsz) (t1ofs+cpsz)
                        else go mba (t0ofs+cpsz) t1ofs -- skip code-point
 
+-- | \(\mathcal{O}(n)\) Strip characters from the beginning end and of 'ShortText' which satisfy given predicate.
+--
+-- >>> dropAround (== ' ') "   white   space   "
+-- "white   space"
+--
+-- >>> dropAround (> 'a') "bcdefghi"
+-- ""
+--
+-- @since 0.1.2
+dropAround :: (Char -> Bool) -> ShortText -> ShortText
+dropAround p t0 = case (mofs1,mofs2) of
+                    (Nothing,_) -> mempty
+                    (Just ofs1,Just ofs2)
+                      | ofs1 == 0, ofs2 == t0sz  -> t0
+                      | ofs1 < ofs2  -> create (ofs2-ofs1) $ \mba -> do
+                          copyByteArray t0 ofs1 mba (B 0) (ofs2-ofs1)
+                    (_,_) -> error "dropAround: the impossible happened"
+  where
+    mofs1 = findOfs    (not . p) t0 (B 0)
+    mofs2 = findOfsRev (not . p) t0 t0sz
+    t0sz = toB t0
+
 ----------------------------------------------------------------------------
 
 -- | Construct a new 'ShortText' from an existing one by slicing