Earlier quoted context omitted.
By the following very short garden path: 1. How silly to write such a thing in C from scratch. Such a project will invariably invent half of Lisp in order to have the right kind of infrastructure for doing this and that. 2. Let's look for some of it up and down the tree. Oh look, there is a bitset and hashmap, see? I don't see test cases for these anywhere; is it original work from this project or battle-tested code…
Why is it silly?
They say it right in the next sentence.