RE: incompatible signatur syntax within instance definition

[Simon Peyton-Jones]

| This is legal in Haskell 98, because the `a' in the inner declaration
is
| implicitly universally quantified.  But if the scope of the outer type
| variable `a' extends over the inner type declaration, then the inner
`a'
| will not be locally universally quantified, and the call to `bar' will
| be a type error, because the `a' in the head of the instance
declaration
| will in general be different than `Int'.
| 
...
| 
| P.S. I note that ghc 5.02.2 enables this extension always, regardless
| of the setting of -fglasgow-exts.  That seems like a bug to me.

And indeed, GHC 6.0 fixes this bug: no scoped type variables without
-fglagow-exts.

Simon
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Fail: unknown exception

[George Russell]

This has to be one of the most irritating ways a program can fall over.
Can't the Haskell RTS try just a /little/ harder to help the poor
programmer?  For example by saying what sort of exception it is, and
(if it's a dynamic exception) what type it has?
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