DynamicAcc: Much progress
DynamicAcc: Handle ECond.  More verbose than I would like.
Experimenting with Layouts to convert variables
Add new, sealed projection function
intermediate checkin... trying to handle variable references.  Maybe need to switch to sealed OpenExp or PreOpenExp rather than Exp.
Trying to play the same tricks with OpenExp as with Exp and finding it more complicated.  Cruft introduced.
Ugly trial and error, fought to get Typeable constraints into some of the Sealed types, did not succeed.
I don't know if this is progress.  Back to needing Typeable for the env, not clear WHY.
Forced through extra typeable constaints
Provide or derive typeable instances.  Dynamic failure when trying to unpack t2b
Improving error messages for projection/layouts
Put in missing PushLayout
Typecheck is happy but it looks like t2b is producing a nonsense result\!
Grows more painful...
A bit more hacking, giving up on this for now.
Refactor: move typecheck pass into its own module in preparation for finishing it.
Wrote part of a real typechecking pass.  Already seeing an additional 12/64 failures as a result\!
Oops, typecheck was supposed to be incomplete, but not through spurious errors.  Fixed one and its down to 5/64 new failures (plus lingering p12 failure on mac only).
Move verifyAccArray to SimpleArray module and add some more checking.
Ah, validation tuned up a bug somewhere else (arrLen).  Fixed.  Now passes 63/64 on mac, and p7 fails.