Re: perplexing syntax-rules bug

[Panicz Maciej Godek <godek.maciek@gmail.com>]

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It doesn't seem to be a bug in syntax-rules. It seems to appear whenever
two consecutive let forms are used with an assoc list argument which starts
with identical elements:

(begin
  (let ((l '((a . X)(b . Y)(c . 7))))
    (assoc-set! l 'b 'Z))
  (let ((l '((a . X)(b . Y))))
    l))
===> ((a . X) (b . Z))

It is likely that the compiler assumes that both lists can be represented
using the same storage, because it doesn't notice that the first object
gets mutated.

This qualifies for a serious bug report, but if you wish to get a quick
workaround, you can do it like this:

(define-syntax sect

  (syntax-rules ()

    ((sect <name> <expr> ...)

     (let* ((sval* '(skip ((name . <name>) (title . #f))))

               (sval (cdr sval*)))

       (format #t "new sect: ~a\n" (quote <name>))

       (format #t "    sval= ~a\n\n" sval)

       (assq-set! sval 'title "ABC")

       (values)))))

Thanks&regards

2014-12-19 21:14 GMT+01:00 Wette, Matthew R (3441) <
matthew.r.wette@jpl.nasa.gov>:

>  Sorry to bug,  I can't figure out why "sval" in the second evaluation of
> "sect" is bound to the "sval" from the first evaluation of "sect".   Anyone
> understand?   This is guile 2.0.11.    -- Matt
>
>  ;; bug_syntax.scm
>
>
>  (define-syntax sect
>
>   (syntax-rules ()
>
>     ((sect <name> <expr> ...)
>
>      (let ((sval '((name . <name>) (title . #f))))
>
>        (format #t "new sect: ~a\n" (quote <name>))
>
>        (format #t "    sval= ~a\n\n" sval)
>
>        (assq-set! sval 'title "ABC")
>
>        (values)))))
>
>
>  (sect one (title "Section One"))
>
> (sect two (title "Section Two"))
>
>  > (load "bug_syntax.scm")
>
>  new sect: one
>
>     sval= ((name . one) (title . #f))
>
>
>  new sect: two
>
>     sval= ((name . two) (title . ABC))
>
>
>
>
>

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