Hi @matias Section 3 of the Honu paper explains how the parser works. https://www.cs.utah.edu/~rafkind/papers/honu-2012.pdf

The parsing phase is interleaved with enforestation and that in turn calls out to user defined macros.

The relevant code begins here: https://github.com/racket/honu/blob/master/honu-parse/parse.rkt