diff --git a/chell.cabal b/chell.cabal
--- a/chell.cabal
+++ b/chell.cabal
@@ -1,5 +1,5 @@
 name: chell
-version: 0.1
+version: 0.1.1
 synopsis: Quiet test runner
 license: MIT
 license-file: license.txt
diff --git a/src/Test/Chell.hs b/src/Test/Chell.hs
--- a/src/Test/Chell.hs
+++ b/src/Test/Chell.hs
@@ -36,6 +36,8 @@
 	, equalWithin
 	, just
 	, nothing
+	, left
+	, right
 	, throws
 	, throwsEq
 	, greater
@@ -63,7 +65,7 @@
 import qualified Control.Applicative
 import qualified Control.Exception
 import           Control.Exception (Exception)
-import           Control.Monad (ap, liftM)
+import           Control.Monad (ap, liftM, when)
 import           Control.Monad.IO.Class (MonadIO, liftIO)
 import qualified Data.Algorithm.Patience as Patience
 import qualified Data.ByteString.Char8
@@ -198,8 +200,8 @@
 		
 		handleJankyIO opts getResult getNotes
 
-addFailure :: Maybe TH.Loc -> Bool -> Text -> Assertions ()
-addFailure maybe_loc fatal msg = Assertions $ \(notes, fs) -> do
+addFailure :: Maybe TH.Loc -> Text -> Assertions ()
+addFailure maybe_loc msg = Assertions $ \(notes, fs) -> do
 	let loc = do
 		th_loc <- maybe_loc
 		return $ Location
@@ -207,22 +209,24 @@
 			, locationModule = Data.Text.pack (TH.loc_module th_loc)
 			, locationLine = toInteger (fst (TH.loc_start th_loc))
 			}
-	return ( if fatal then Nothing else Just ()
-	       , (notes, Failure loc msg : fs))
+	return (Just (), (notes, Failure loc msg : fs))
 
+die :: Assertions a
+die = Assertions (\s -> return (Nothing, s))
+
 -- | Cause a test to immediately fail, with a message.
 --
 -- 'fail' is a Template Haskell macro, to retain the source-file location
 -- from which it was used. Its effective type is:
 --
 -- @
--- $fail :: 'Text' -> 'Assertions' ()
+-- $fail :: 'Text' -> 'Assertions' a
 -- @
-fail :: TH.Q TH.Exp -- :: Text -> Assertions ()
+fail :: TH.Q TH.Exp -- :: Text -> Assertions a
 fail = do
 	loc <- TH.location
 	let qloc = liftLoc loc
-	[| addFailure (Just $qloc) True |]
+	[| \msg -> addFailure (Just $qloc) msg >> die |]
 
 -- | Print a message from within a test. This is just a helper for debugging,
 -- so you don't have to import @Debug.Trace@.
@@ -249,7 +253,9 @@
 	result <- liftIO io
 	case result of
 		AssertionPassed -> return ()
-		AssertionFailed err -> addFailure (Just loc) fatal err
+		AssertionFailed err -> do
+			addFailure (Just loc) err
+			when fatal die
 
 -- | Run an 'Assertion'. If the assertion fails, the test will immediately
 -- fail.
@@ -308,6 +314,18 @@
 -- | Assert that some value is @Nothing@.
 nothing :: Maybe a -> Assertion
 nothing x = pure (isNothing x) ("nothing: received Just")
+
+-- | Assert that some value is @Left@.
+left :: Either a b -> Assertion
+left x = pure (isLeft x) ("left: received Right") where
+	isLeft (Left _) = True
+	isLeft (Right _) = False
+
+-- | Assert that some value is @Right@.
+right :: Either a b -> Assertion
+right x = pure (isRight x) ("right: received Left") where
+	isRight (Left _) = False
+	isRight (Right _) = True
 
 -- | Assert that some computation throws an exception matching the provided
 -- predicate. This is mostly useful for exception types which do not have an