diff --git a/simple-parser.cabal b/simple-parser.cabal
--- a/simple-parser.cabal
+++ b/simple-parser.cabal
@@ -4,10 +4,10 @@
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: cae86899037beab7723314f49d8129dda7254a4261348de1d4b2e5ed8ebde7bf
+-- hash: 05dbeeb0f7613ae6d38c54b0654472b0b1d48dc401b57a41cae0dc16554fb065
 
 name:           simple-parser
-version:        0.2.1
+version:        0.2.2
 synopsis:       Simple parser combinators
 description:    Please see the README on GitHub at <https://github.com/ejconlon/simple-parser#readme>
 category:       Parsing
@@ -44,6 +44,7 @@
       base >=4.12 && <5
     , containers >=0.6 && <0.7
     , list-t >=1.0 && <1.1
+    , mmorph >=1.1 && <1.2
     , mtl >=2.2 && <2.3
     , text >=1.2 && <1.3
   default-language: Haskell2010
@@ -61,6 +62,7 @@
       base >=4.12 && <5
     , containers >=0.6 && <0.7
     , list-t >=1.0 && <1.1
+    , mmorph >=1.1 && <1.2
     , mtl >=2.2 && <2.3
     , simple-parser
     , tasty
diff --git a/src/SimpleParser.hs b/src/SimpleParser.hs
--- a/src/SimpleParser.hs
+++ b/src/SimpleParser.hs
@@ -1,6 +1,8 @@
--- | Re-exports for all modules. See 'SimpleParser.Examples.Json' or the test suit for examples,
--- 'SimpleParser.Parser' for the core transformer, 'SimpleParser.Stream' for the source abstraction,
--- or 'SimpleParser.Input' for useful combinators.
+-- | This is basically a simpler and slower (Mega)Parsec that is fully backtracking by default.
+--
+-- The root module re-exports all modules. See "SimpleParser.Examples.Json" or the test suit for examples,
+-- "SimpleParser.Parser" for the core transformer, "SimpleParser.Stream" for the source abstraction,
+-- or "SimpleParser.Input" for useful combinators.
 module SimpleParser
   ( module SimpleParser.Input
   , module SimpleParser.Parser
diff --git a/src/SimpleParser/Examples/Json.hs b/src/SimpleParser/Examples/Json.hs
--- a/src/SimpleParser/Examples/Json.hs
+++ b/src/SimpleParser/Examples/Json.hs
@@ -9,7 +9,6 @@
 import Control.Applicative (empty)
 import Control.Monad (void)
 import Data.Char (isSpace)
-import Data.Foldable (asum)
 import Data.Text (Text)
 import Data.Void (Void)
 import SimpleParser
@@ -104,7 +103,7 @@
 nullParser = JsonNull <$ nullTok
 
 boolParser :: JsonParser (JsonF a)
-boolParser = branchParser [JsonBool True <$ trueTok, JsonBool False <$ falseTok]
+boolParser = isolateParser (branchParser [JsonBool True <$ trueTok, JsonBool False <$ falseTok])
 
 objectPairParser :: JsonParser a -> JsonParser (String, a)
 objectPairParser root = do
@@ -120,7 +119,7 @@
 arrayParser root = jsonBetween openBracket closeBracket (fmap JsonArray (jsonSepBy root comma))
 
 rootParser :: JsonParser a -> JsonParser (JsonF a)
-rootParser root = asum opts where
+rootParser root = isolateParser (branchParser opts) where
   pairParser = objectPairParser root
   opts =
     [ objectParser pairParser
diff --git a/src/SimpleParser/Parser.hs b/src/SimpleParser/Parser.hs
--- a/src/SimpleParser/Parser.hs
+++ b/src/SimpleParser/Parser.hs
@@ -7,6 +7,7 @@
   , reflectParser
   , branchParser
   , suppressParser
+  , isolateParser
   , defaultParser
   , optionalParser
   , silenceParser
@@ -14,12 +15,14 @@
   , greedyStarParser_
   , greedyPlusParser
   , greedyPlusParser_
+  , lookAheadParser
   ) where
 
 import Control.Applicative (Alternative (..), liftA2)
 import Control.Monad (MonadPlus (..), ap, (>=>))
 import Control.Monad.Except (MonadError (..))
 import Control.Monad.Identity (Identity (..))
+import Control.Monad.Morph (MFunctor (..))
 import Control.Monad.State (MonadState (..))
 import Control.Monad.Trans (MonadTrans (..))
 import Data.Foldable (toList)
@@ -73,6 +76,9 @@
 instance MonadTrans (ParserT e s) where
   lift ma = ParserT (\s -> lift (fmap (\a -> ParseResult (ParseSuccess a) s) ma))
 
+instance MFunctor (ParserT e s) where
+  hoist trans (ParserT f) = ParserT (hoist trans . f)
+
 -- | Runs a non-effectful parser from an inital state and collects all results.
 runParser :: Parser e s a -> s -> [ParseResult e s a]
 runParser m s = runIdentity (ListT.toList (runParserT m s))
@@ -100,6 +106,7 @@
         pure (Just (ParseResult (ParseSuccess v) t, ListT (go rest)))
 
 -- | Combines the results of many parsers.
+-- Equvalent to 'asum'.
 branchParser :: (Foldable f, Monad m) => f (ParserT e s m a) -> ParserT e s m a
 branchParser = start . toList where
   start ps =
@@ -115,10 +122,8 @@
           r:rs -> run s r rs
       Just (a, rest) -> pure (Just (a, rest))
 
--- | If the parse results in ANY successes, keep only those. Otherwise return all failures.
--- This may block indefinitely as it awaits either the end of the parser or its first success.
-suppressParser :: Monad m => ParserT e s m a -> ParserT e s m a
-suppressParser parser = ParserT (ListT . go [] . runParserT parser) where
+gatherParser :: Monad m => Bool -> ParserT e s m a -> ParserT e s m a
+gatherParser single parser = ParserT (ListT . go [] . runParserT parser) where
   go !acc listt = do
     m <- ListT.uncons listt
     case m of
@@ -126,7 +131,9 @@
       Just (r@(ParseResult v _), rest) ->
         case v of
           ParseError _ -> go (r:acc) rest
-          ParseSuccess _ -> pure (Just (r, ListT (filterOk rest)))
+          ParseSuccess _ ->
+            let t = if single then empty else ListT (filterOk rest)
+            in pure (Just (r, t))
 
   returnErr racc =
     case racc of
@@ -143,6 +150,18 @@
           ParseError _ -> nextListt
           ParseSuccess _ -> pure (Just (r, ListT nextListt))
 
+-- | If the parse results in ANY successes, keep only those. Otherwise return all failures.
+-- This may block indefinitely as it awaits either the end of the parser or its first success.
+-- See 'isolateParser' if you want only one success.
+suppressParser :: Monad m => ParserT e s m a -> ParserT e s m a
+suppressParser = gatherParser False
+
+-- | If the parse results in ANY successes, keep only THE FIRST. Otherwise return all failures.
+-- This may block indefinitely as it awaits either the end of the parser or its first success.
+-- See 'suppressParser' if you want all successes.
+isolateParser :: Monad m => ParserT e s m a -> ParserT e s m a
+isolateParser = gatherParser True
+
 -- | If the parser yields no results (success or failure), yield a given value.
 defaultParser :: Monad m => a -> ParserT e s m a -> ParserT e s m a
 defaultParser def parser = ParserT (\s -> ListT (go s (runParserT parser s))) where
@@ -158,6 +177,7 @@
 optionalParser parser = defaultParser Nothing (fmap Just parser)
 
 -- | Removes all failures from the parse results.
+-- Equivalent to 'catchError (const empty)'.
 silenceParser :: Monad m => ParserT e s m a -> ParserT e s m a
 silenceParser parser = ParserT (ListT . go . runParserT parser) where
   go listt = do
@@ -197,3 +217,13 @@
 -- | Same as 'greedyPlusParser' but discards the result.
 greedyPlusParser_ :: Monad m => ParserT e s m a -> ParserT e s m ()
 greedyPlusParser_ parser = parser *> greedyStarParser_ parser
+
+-- | Yield the results of the given parser, but rewind back to the starting state.
+-- Note that these results may contain errors, so you may want to stifle them with 'silenceParser', for example.
+lookAheadParser :: Monad m => ParserT e s m a -> ParserT e s m a
+lookAheadParser parser = do
+  s <- get
+  flip catchError (\e -> put s *> throwError e) $ do
+    v <- parser
+    put s
+    pure v
diff --git a/src/SimpleParser/Stream.hs b/src/SimpleParser/Stream.hs
--- a/src/SimpleParser/Stream.hs
+++ b/src/SimpleParser/Stream.hs
@@ -1,5 +1,5 @@
 -- | This reworks 'Text.Megaparsec.Stream' to split interfaces.
--- See https://hackage.haskell.org/package/megaparsec-9.0.1/docs/Text-Megaparsec-Stream.html
+-- See <https://hackage.haskell.org/package/megaparsec-9.0.1/docs/Text-Megaparsec-Stream.html Text.Megaparsec.Stream>.
 module SimpleParser.Stream
   ( Chunked (..)
   , Stream (..)
diff --git a/test/Main.hs b/test/Main.hs
--- a/test/Main.hs
+++ b/test/Main.hs
@@ -425,6 +425,44 @@
         ]
   in testParserTrees parser cases
 
+test_isolate_success :: [TestTree]
+test_isolate_success =
+  let state = OffsetStream 0 "hi"
+      parser = isolateParser (asum [pure 1, pure 2]) :: TestParser Int
+      cases =
+        [ ("non-empty", InputOutput "hi" [parseSuccessResult 1 state])
+        ]
+  in testParserTrees parser cases
+
+test_isolate_fail_first :: [TestTree]
+test_isolate_fail_first =
+  let err = Error "boo"
+      parser = isolateParser (asum [throwError err, pure 2]) :: TestParser Int
+      cases =
+        [ ("non-empty", InputOutput "hi" [parseSuccessResult 2 (OffsetStream 0 "hi")])
+        ]
+  in testParserTrees parser cases
+
+test_isolate_fail_second :: [TestTree]
+test_isolate_fail_second =
+  let err = Error "boo"
+      parser = isolateParser (asum [pure 1, throwError err]) :: TestParser Int
+      cases =
+        [ ("non-empty", InputOutput "hi" [parseSuccessResult 1 (OffsetStream 0 "hi")])
+        ]
+  in testParserTrees parser cases
+
+test_isolate_fail_both :: [TestTree]
+test_isolate_fail_both =
+  let state = OffsetStream 0 "hi"
+      err1 = Error "boo1"
+      err2 = Error "boo2"
+      parser = isolateParser (asum [throwError err1, throwError err2]) :: TestParser Int
+      cases =
+        [ ("non-empty", InputOutput "hi" [parseErrorResult err1 state, parseErrorResult err2 state])
+        ]
+  in testParserTrees parser cases
+
 test_silence_success :: [TestTree]
 test_silence_success =
   let state = OffsetStream 0 "hi"
@@ -459,6 +497,25 @@
       parser = silenceParser (asum [throwError err1, throwError err2]) :: TestParser Int
       cases =
         [ ("non-empty", InputOutput "hi" [])
+        ]
+  in testParserTrees parser cases
+
+test_look_ahead_success :: [TestTree]
+test_look_ahead_success =
+  let parser = lookAheadParser anyToken
+      cases =
+        [ ("empty", InputOutput "" [])
+        , ("non-empty", InputOutput "hi" [parseSuccessResult 'h' (OffsetStream 0 "hi")])
+        ]
+  in testParserTrees parser cases
+
+test_look_ahead_failure :: [TestTree]
+test_look_ahead_failure =
+  let err = Error "boo"
+      parser = lookAheadParser (anyToken *> throwError err) :: TestParser Char
+      cases =
+        [ ("empty", InputOutput "" [])
+        , ("non-empty", InputOutput "hi" [parseErrorResult err (OffsetStream 0 "hi")])
         ]
   in testParserTrees parser cases