Merge pull request #456 from ocramz/master

add foldWhile
snoyberg · Nov 25, 2020 · 0bf72ae · 0bf72ae
2 parents 2f9e868 + cd3c7c8
commit 0bf72ae
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diff --git a/conduit/ChangeLog.md b/conduit/ChangeLog.md
@@ -1,5 +1,9 @@
 # ChangeLog for conduit
 
+## 1.3.4
+
+* Add `foldWhile` [#453](https://github.com/snoyberg/conduit/issues/453) [#456](https://github.com/snoyberg/conduit/pull/456).
+
 ## 1.3.3
 
 * Add `uncons`, `unconsM`, `unconsEither`, `unconsEitherM`.

diff --git a/conduit/conduit.cabal b/conduit/conduit.cabal
@@ -1,5 +1,5 @@
 Name:                conduit
-Version:             1.3.3
+Version:             1.3.4
 Synopsis:            Streaming data processing library.
 description:
     `conduit` is a solution to the streaming data problem, allowing for production,

diff --git a/conduit/src/Data/Conduit/Combinators.hs b/conduit/src/Data/Conduit/Combinators.hs
@@ -62,6 +62,7 @@ module Data.Conduit.Combinators
     , foldlE
     , foldMap
     , foldMapE
+    , foldWhile
     , all
     , allE
     , any
@@ -1755,6 +1756,19 @@ mapAccumWhileC f =
 {-# INLINE mapAccumWhileC #-}
 STREAMING(mapAccumWhile, mapAccumWhileC, mapAccumWhileS, f s)
 
+
+-- | Specialized version of 'mapAccumWhile' that does not provide values downstream.
+--
+-- @since 1.3.4
+foldWhile :: Monad m => (a -> s -> Either e s) -> s -> ConduitT a o m (Either e s)
+foldWhile f = loop
+  where
+    loop !s = await >>= maybe (return $ Right s) go
+      where
+        go a = either (return . Left $!) loop $ f a s
+{-# INLINE foldWhile #-}
+
+
 -- | 'concatMap' with an accumulator.
 --
 -- Subject to fusion