On 08/30/2012 05:51 AM, David A. Wheeler wrote:
> John Cowan:
>> Note that having a portable implementation of R7RS `equal?` is not an
>> issue, as all implementations are expected to provide it. They may also
>> (as Chibi does) also provide the R5RS `equal?` function in a different
>> library.
>
> Okay. I still think it's important that the spec clearly state what happens
> if a cycle is detected by "equal?". I recommend text like "If a cycle is
> detected, #f is returned." I'm guessing that's what many implementations
> with cycle-detection do (is that true?).
No, that would be wrong if both operands have "equivalent" cycles.
(equal? '#1=(x . #1#) '#2=(x x . #2#))
This must return #t *if* it returns without an error.
An implementation might be allowed to *not* return
(loop indefinitely or throw an exception), but not to return #f
in this case.
If equals? terminates, it must return the correct result.
--
--Per Bothner
[email protected] http://per.bothner.com/
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