Re: incompatible signatur syntax within instance definition

Christian Maeder 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