On: Ask HN: programming languages written in JavaScript?

I'm not really sure but maybe ... processing.js ? http://ejohn.org/blog/processingjs/

I think it can serve as an example.

If you count Processing.js, there's also ArcLite:

http://jonathan.tang.name/code/arclite

Processing.js may not be the best example for new language implementers, because the compiler is implemented with regexp search & replace. That makes it fairly fast, but difficult to extend and almost impossible for a neophyte to read.