Re: Deep fmap with GADTs and type families.

David Menendez:

On Thu, Mar 5, 2009 at 10:07 PM, Dan Doel wrote:

...

But we've so far not been able to find a way of merely annotating the original into working. So, I was wondering if any of the more knowledgeable folks here could illuminate what's going wrong here, and whether I should expect my original code to work or not.

I'll bet the problem has to do with the fact that "f" only appears in "Nest n f a", so the type checker can't figure out what "f" is.

Exactly. In other words, the signature is ambiguous. Manuel