Don't just have a placeholder. While this doesn't have a huge effect (if
any) on performance, it does generate smaller output for Chez to
process, and is tidier. Perhaps it's good for other back ends too, ones
that don't optimise as much as Chez does.
Only doing named functions, not higher order functions. HOFs may be
worth doing too, if we can, since this could remove lambdas and make
fewer closures.
The increment in TTC Version is necessary because otherwise there could
be inconsistencies between libraries and clients erasure properties.
If all branches in a case block are a lambda, lift the lambda out. In
many cases, this can save creating a closure then evaluating it
immediately, because the function is already applied to the extra
argument.
This happens in particular with IO based code, where the extra argument
is the world token. One place where this transformation has a big effect
is 'evalRef' so the evaluator is now a bit faster (about 20% on the
small benchmark I tried it on - but no guarantees that's going to happen
on other examples!)
