[gambit-list] Gambit-C 4.0 beta 18
Bradley Lucier
lucier at math.purdue.edu
Mon Sep 25 11:41:40 EDT 2006
On Sep 25, 2006, at 10:07 AM, Marc Feeley wrote:
> On 23-Sep-06, at 4:29 PM, Bradley Lucier wrote:
>
>> Marc:
>>
>> I found a few more problems---in FIXLENGTH you want to set ___temp
>> to -___temp (not ~temp) when ___temp is negative (try (fxlength -1)),
>
> This is incorrect.
Well, it may be incorrect that you want it, but otherwise it's a
matter of convention.
> Note that the definition of fxlength in R6RS uses ~temp (SRFI 77
> erroneously used -temp). With ~temp it matches the Common Lisp
> semantics, i.e. (fxlength -1) = 0.
Gotcha. I was looking at the SRFI-77 code.
>
>> This has been rather extensively tested on 32-bit (ppc) and 64-bit
>> (x86-64) platforms by comparing it with the R6RS definitions of
>> the same functions. The diff is from the original gambit.h.
>
> For (fxfirst-bit-set 0) the R6RS specifies that -1 should be
> returned. I see no reason why -1 should be viewed as the correct
> answer. It seems too arbitrary. The "Scheme way" is to return #f,
> in fact that's what Gambit's (first-set-bit 0) returns. What do
> you think?
Well, I don't know ... Clinger made a lot of noise during the
SRFI-77 process about making numerical code more conducive to type
checking. Having functions return {#f}\union{numbers} is useful and
Schemely, but using a numeric code is also useful.
Perhaps you should send a comment to R6RS to get (fx-first-bit-set 0)
=> #f if you believe strongly that it should be changed. In the end,
though, I think Gambit should have the R6RS semantics for this function.
Brad
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