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Re: Nyacc: how to lex comments?

From: Matt Wette
Subject: Re: Nyacc: how to lex comments?
Date: Mon, 16 Mar 2020 17:11:59 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1

On 3/16/20 2:39 PM, address@hidden wrote:

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

make-comm-reader will not eat newlines at end of comment by default.
If you want the comment # ... \n to include the newline try adding #:eat-newline #t.


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