Yes, Chez Scheme is mostly written in itself, including most primitives and the entire compiler. Additionally, the way Racket CS is architected, significant par

Yes, Chez Scheme is mostly written in itself, including most primitives and the entire compiler. Additionally, the way Racket CS is architected, significant parts of the C-implemented Racket runtime are instead written in Racket and compiled to Chez Scheme ahead of time, such as the thread system and the IO library.