Re: Concept[T] design question

[jcosborn]

In the case of `proc f(x: Has[seq[any]])`, could you first try matching against 
the generic `Has[T]`, let the concept body define `T`, then extract its value 
and compare that against `seq[any]` to see if it matches? At that point if the 
type constraint was `Has[seq[S]]` you could match to bind `S` too.