polyEqual

[Stephen Weeks]

> Steve, you'll probably want to look at DirectExp sometime.  I'm debating
> changing the send* functions from 
> t * ??? -> Label.t * Block.t list 
> to 
> t * ??? -> Block.t list 
> and let it implicit that the start label is the label of the first block
> in the list. 

I took a quick look and it seems fine.  I don't have any strong
feelings one way or the other on the send* stuff.  I lean slightly
towards keeping it the way it is.

I had thought a bit about this code, and my current feeling is that if
I were to rewrite it, I would make the DirectExp syntax tree an
explicit datatype, and move the linearization algorithm all into one
place.  Using all the higher-order stuff is cute, but I don't think it
really buys much, and I think it is harder to understand.  It would at
least make an interesting comparison.