Refactor compiler infrastructure.
Rename a few types.
Prototype function calls.
Start to build closures.
Continue prototyping lambdas and closures, not done.
Introduce lambda rewriter.
Variable assignments. Typed parameters.  Field definitions and other type-related codegen.
Expression sequences.
Lambda rewriting prototype.
Perform rewriting. Not working yet.
Try using a comp-expr to wrap up both rewritten expressions and new types.
Implement full rewriting infrastructure.
Working on closures.
Works@!