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Nyacc: how to lex comments?

From: tomas
Subject: Nyacc: how to lex comments?
Date: Mon, 16 Mar 2020 22:39:41 +0100
User-agent: Mutt/1.5.21 (2010-09-15)


in my quest to play parsing, I'm failing when I try to cope with

Here's an excerpt from my current file

    (define my-grammar
       (start my-file)
        ;; boring grammar details elided
    (define mach (make-lalr-machine aq-grammar))
    (define mtab (lalr-match-table mach))
    (define gen-lexer (make-lexer-generator mtab
                       #:comm-reader (make-comm-reader '(("#" . "\n")))))
    (define raw-parse (make-lalr-parser mach))
    (define (parse) (raw-parse (gen-lexer)))
    ;; (gen-lexer)

Comments are shell-like, from "#" to end of line. Grammar
works fine so-far, but when (parse) sees a hash-comment
(even just a one-line input

  # this is a comment

it panics:

    In ice-9/boot-9.scm:
      1736:10  6 (with-exception-handler _ _ #:unwind? _ # _)
    In unknown file:
               5 (apply-smob/0 #<thunk 557754319740>)
    In ice-9/boot-9.scm:
        718:2  4 (call-with-prompt ("prompt") #<procedure 5577543308e0 …> …)
    In ice-9/eval.scm:
        619:8  3 (_ #(#(#<directory (guile-user) 5577543c1f00>)))
    In ice-9/boot-9.scm:
       2806:4  2 (save-module-excursion #<procedure 5577543b31b0 at ice-…>)
      4351:12  1 (_)
    In nyacc/parse.scm:
         78:4  0 (_ _ #:debug _)
    nyacc/parse.scm:78:4: Throw to key `nyacc-error' with args `("~A:~A: parse 
failed at state ~A, on input ~S" "(unknown)" 1 0 " a comment")'.

I feel I'm doing something stupid. What can I do to understand
what's going on?

Thanks & cheers
-- tomás

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