[gambit-list] how does make-default-entry-hook work?

In lib/_repl.scm: (define-prim (##make-default-entry-hook) (let ((settings (##vector #f #f))) (lambda (proc args execute) (if (##vector-ref settings 0) (##step-on)) ;; turn on single-stepping (if (##vector-ref settings 1) (##trace-generate (##make-call-form proc (##argument-list-remove-absent! args '()) ##max-fixnum) execute #f) (execute))))) how does this code work at all? isn't settings #f #f, which would mean the first if does nothing, and the first part of the second if also does nothing? is there some funky dynamic-wind / dynamic scope going on here?