incompatible signatur syntax within instance definition

[Malcolm Wallace]

Christian Maeder <maeder at tzi.de> writes:

> Fergus Henderson wrote:
> > I think the issue here is that in ghc (with -fglasgow-exts),
> > the "a" here refers to the same type variable "a" in the
> > top of the instance declaration, which has already been
> > constained, and cannot be constrained again.
> 
> Is that a bug or a feature?

It is a feature called "scoped type variables".

Regards,
    Malcolm