I found the root bug, I think, flagged by this message:

scheme@(guile-user)> (define-tokenizer tokiz ("[a-z]+" #\a))

While compiling expression:

ERROR: build-constant-store: unrecognized object #<procedure make-regexp (_ . _)>

I was putting procedure-objects in the macro when I should have been putting in syntax.

works:

(list

(datum->syntax (car cz) 'make-regexp)

(string-append

"^" (syntax->datum (car cz)))))

broken (but worked in guile 1.8.8):

(list

make-regexp

(list string-append "^" (car cz))))

Matt