Re: Nyacc: how to lex comments?

[Matt Wette <matt.wette@gmail.com>]

On 3/16/20 2:39 PM, tomas@tuxteam.de wrote:
> Hi,
>
> in my quest to play parsing, I'm failing when I try to cope with
> comments.
>
> Here's an excerpt from my current file
>
>      (define my-grammar
>        (lalr-spec
>         (start my-file)
>         (grammar
>          ;; 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)
>      (parse)
>
> 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:
>
>      Backtrace:
>      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.

Matt