Generalise the type of mapException; pointed out by Isaac Dupree

[ghc-base.git] / Control / Exception.hs

diff --git a/Control/Exception.hs b/Control/Exception.hs
index b3638f6..812c165 100644 (file)
--- a/Control/Exception.hs
+++ b/Control/Exception.hs
@@ -358,7 +358,7 @@ handleJust p =  flip (catchJust p)
 
 -- Notice that the usage of 'unsafePerformIO' is safe here.
 
-mapException :: Exception e => (e -> e) -> a -> a
+mapException :: (Exception e1, Exception e2) => (e1 -> e2) -> a -> a
 mapException f v = unsafePerformIO (catch (evaluate v)
                                           (\x -> throw (f x)))