[Bug-kawa] [bug #27042] Bad interaction between syntax-rules and call-with-values

[Helmut Eller]

URL:
  <http://savannah.gnu.org/bugs/?27042>

                 Summary: Bad interaction between syntax-rules and
call-with-values
                 Project: Kawa
            Submitted by: ellerh
            Submitted on: Thu 16 Jul 2009 05:53:09 PM GMT
                Category: None
                Severity: 3 - Normal
              Item Group: None
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any

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Details:

This example 

(let-syntax ((dlet
              (syntax-rules ()
                ((dlet (var val) body)
                 (let ((saved var))
                   (set! var val)
                   (call-with-values (lambda () body)
                     (lambda (result)
                       (set! var saved)
                       result)))))))
  (let ((x 0))
    (list x
          (dlet (x (+ x 10))
                x)
          x)))

should return (0 10 0) but returns (0 10 10).  
The intention of dlet is to temporarily rebind the variable.
Sorry, couldn't come up with a simpler expression.

If it helps: referencing var inside the second lambda, e.g. with
something like (set! var var), works around the problem.





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