[MLton] modifying flatten.fun to always flatten

[Matthew Fluet]

> I ran into acouple problems adopting the first approach, so I have
> implimented the second approach. It seems to be doing what I need it to do
> and the compiler fixpoints. I would like to know if there is a way to
> print the ssa tree to a file before and after the flatten pass. Bassically
> I just want to double check I am correctly flattening all tupples.

-keep-pass flatten  will leave you with z.flatten.pre.ssa and
z.flatten.post.ssa.  The argument to -keep-pass is actually a regular
expression (useful for the passes that are run more than once).  Compiling
with  -show-types true  will probably also be useful to you; you'll be
able to search for * types in the post.ssa.