Chris Krycho, a person I really respect, is learning Racket to build programming languages. Racket is generally slotted as a language to build languages. The popular books focus on Racket innovations related to constructing Domain Specific Languages. This include hygienic macros, the Racket loading and evaluation phases and the module system. While it is uniquely suited for creating languages 1, Racket is also a research vehicle for a large body of programming language research.