Hi,
Marco Maggi <marco.maggi-i...@poste.it> writes:
> Mark H Weaver wrote:
>> While reading psyntax.scm, I noticed that the definition of 'bound-id=?'
>> does not match the definition in "Syntax Abstraction in Scheme" by
>> Dybvig, Hieb, and Bruggeman.
>>
>> The paper states "Two identifiers that are bound-identifier=? are also
>> free-identifier=?".
>
> I think you are referring to this paragraph from the paper[1] (page 12):
>
> Two identifiers that are bound-identifier=? are also
> free-identifier=?, but two identifiers that are free-identifier=?
> may not be bound-identifier=?. An identifier introduced by a macro
> transformer may refer to the same enclosing binding as an identifier
> not introduced by the transformer, but an introduced binding for one
> will not capture references to the other.
Yes.
>> The following expression shows that this is not the case in Guile 2.0:
>>
>> (let* ((x 1) (s1 #'x)
>> (x 2) (s2 #'x))
>> (list (bound-identifier=? s1 s2)
>> (free-identifier=? s1 s2)))
>> => (#t #f)
>
> The expander in Ikarus/Vicare also returns this value.
I think that indicates a bug in Ikarus/Vicare.
>> Racket reports (#f #f) for the same expression.
>
> Racket is different because its expander implements a variant of phase
> separation; if the whole form is evaluated at phase N, the "x" in "#'x"
> should be searched among the bindings at phase N-1 (if any)
I don't see how that's relevant to this example.
> Your code works, but when you actually try to use the
> identifiers for something:
>
> #!r6rs
> (import (rnrs))
> (define-syntax doit
> (lambda (stx)
> (let* ((x 1) (s1 #'x)
> (x 2) (s2 #'x))
> #`(let ((#,s1 123))
> #,s2))))
> (doit)
Whether #`(let ((#,s1 123)) #,s2) works is equivalent to asking whether
s1 and s2 are 'bound-identifier=?', by definition. That's precisely
what 'bound-identifier=?' is supposed to be used for: to determine
whether a binding for one should capture the other.
I don't see why you think #`(let ((#,s1 123)) #,s2) should work. Why
would you use two identifiers with different binding names (s1 and s2)
to construct that code? Can you construct a more realistic example?
Thanks,
Mark
