My Scheme compiler frontend is almost at the point where I can move my focus from syntax to semantics. It successfully recognizes 100% of the Scheme grammar's tokens and constructs an AST representation for about 75% of the constructs available in R5RS. Along with this lexer/parser comes a simple toplevel read-parse-print console that parses stdin or file input and, rather than evaluating it, just prints the AST out for inspection. This has been really useful for debugging. I also have some unit tests that validate certain Scheme input produces the expect tree, also proving to be rather useful. A test is written first for the construct I'm attempting to parse, and I know I'm pretty much there when it succeeds. Very nice.

Obviously most of the difficult tasks are still to come. I've done some work on the backend, but more experimentation than anything else. Most of my time here has been spent thinking about how to make interoperability with other “mainstream” managed languages palatable. I'm actually writing this so that it's pretty modular, thinking this would facilitate plugging in different steps along the way (e.g. so that extending it with an optimizer is easy; ripping an optimizer out and tossing a more efficient one in is even simpler).

Wish I had more time to throw at this. Some day. :)