[Grace-core] Lists and filter

[Marco Servetto]

All the things that you mention in this email are about effifiency,
thus against the design goals of grace, to be a teaching language.
we want collections to be the simplest, most predictable and most
flexible and (thus) slowest things ever. Right?
I understand iterators usually do not have support for random access and so on.
The problem is why the do not offer it. They could.