tuples: data structure separation from trees

[Aldy Hernandez]

> There are a lot of us that are happy to devote time and people
> resources to helping you with this (both design and implementation),
> so if you feel like you don't have time to go look at other IR's or
> something, please let us help :)

That would be great, especially the bit about looking at other IRs.
Diego said he'd look into this, so you'd have to coordinate with him too.

Aldy