Oh dear, that really is quite a strange error message. Something is definitely wrong. Can you please make a ticket for it, and include instructions on how to reproduce it? I gather that it depends on other packages that themselves needed changes, so reproduction might not be entirely easy? Simon | -----Original Message----- | From: glasgow-haskell-users-bounces@haskell.org [mailto:glasgow-haskell-users- | bounces@haskell.org] On Behalf Of Malte Sommerkorn | Sent: 29 September 2010 19:50 | To: glasgow-haskell-users@haskell.org | Subject: GHC 7.0.1 rc1: Could not deduce (Typeable a) from the context (Typeable a, | …) | | While compile failures were easy to fix for syb, X11 and xmonad, here's a more | mysterious encounter with xmonad-contrib. The module in question is | | http://code.haskell.org/XMonadContrib/XMonad/Layout/MultiToggle.hs | | and the rest of this mail is the error: | | XMonad/Layout/MultiToggle.hs:194:30: | Could not deduce (Typeable a) | from the context (Typeable a, Show ts, HList ts a, LayoutClass l a) | arising from a use of `fromMessage' | Possible fix: | add (Typeable a) to the context of the instance declaration | In a stmt of a pattern guard for | an equation for `handleMessage': | Just (Toggle t) <- fromMessage m | In an equation for `handleMessage': | handleMessage mt m | | Just (Toggle t) <- fromMessage m, | i@(Just _) <- find (transformers mt) t | = case currLayout mt of { | EL l det | -> do { l' <- fromMaybe l | `fmap` | handleMessage l (SomeMessage ReleaseResources); | .... } | where | cur = (i == currIndex mt) } | | otherwise | = case currLayout mt of { | EL l det | -> fmap (fmap (\ x -> mt {currLayout = EL x det})) | $ handleMessage l m } | In the instance declaration for `LayoutClass (MultiToggle ts l) a' | | XMonad/Layout/MultiToggle.hs:195:25: | Could not deduce (HList ts a) | from the context (Typeable a, | Show ts, | HList ts a, | LayoutClass l a, | Transformer t a) | arising from a use of `find' | Possible fix: | add (HList ts a) to the context of | the data constructor `Toggle' | or the instance declaration | In a stmt of a pattern guard for | an equation for `handleMessage': | i@(Just _) <- find (transformers mt) t | In a stmt of a pattern guard for | an equation for `handleMessage': | Just (Toggle t) <- fromMessage m | In an equation for `handleMessage': | handleMessage mt m | | Just (Toggle t) <- fromMessage m, | i@(Just _) <- find (transformers mt) t | = case currLayout mt of { | EL l det | -> do { l' <- fromMaybe l | `fmap` | handleMessage l (SomeMessage ReleaseResources); | .... } | where | cur = (i == currIndex mt) } | | otherwise | = case currLayout mt of { | EL l det | -> fmap (fmap (\ x -> mt {currLayout = EL x det})) | $ handleMessage l m } | | _______________________________________________ | Glasgow-haskell-users mailing list | Glasgow-haskell-users@haskell.org | http://www.haskell.org/mailman/listinfo/glasgow-haskell-users