Still doesn't fix it.
Does not fix the lack of source location in errors.
These are tied to the PICOBOARD2 hardware, and thus are not of general interest.
Previous fix (no fvs) was bogus. Fixing the env bug in the parser is the real fix.
Otherwise, immutable locals will have no definition site.
Will make the pretty-printer available when debugging ast.rkt.
This allows some eta-expansion inlinings that wouldn't have worked otherwise.
This makes it unnecessary to always have a begin inside lambdas.