| So the 'where' binding in the following does not get generalized | because it could not have been written at the top level, correct? The other way round. 'where' bindings that could have been written at top level *are* generalised; ones that could not are *not* generalised. See "Which bindings are affected?" in http://hackage.haskell.org/trac/ghc/blog/LetGeneralisationInGhc7, which tries to be precise. If it's hard to understand can I make it easier? Simon | | >>>>> | cast :: (Typeable a, Typeable b) => a -> Maybe b | cast x = r | where | r = if typeOf x == typeOf (fromJust r) | then Just $ unsafeCoerce x | else Nothing | <<<<< | | > Why the change. You'll remember that over the last year GHC has changed not | to generalise local lets: | http://hackage.haskell.org/trac/ghc/blog/LetGeneralisationInGhc7 | > | > I relaxed the rule in 7.2, as discussed in "Which bindings are affected?" | in that post. For reasons I have not investigated, 7.2 *still* doesn't | generalise 'result'; but 7.4 correctly does. | > | > Simon