Re: [Sbcl-devel] rejected patch: "Bug 106 (COMPLEX type specifiers)"

[Christophe R. <cs...@ca...>]

On Mon, Jan 21, 2002 at 01:40:25PM -0600, William Harold Newman wrote:
> Back in October (predating the death of my old laptop mail machine,
> so this isn't a proper reply-to-ish reply to the original message)
> Christophe Rhodes sent "a rough patch to fix bug 106".
> 
> I'm going to reject it because it seems to be wrong in some details.
> In particular, after the patch we have
>   * (sb-kernel:specifier-type '(complex (member 6 9)))
>   #<SB-KERNEL:NUMERIC-TYPE (COMPLEX RATIONAL)>
> so that
>   * (typep (complex 1/2 3/2) '(complex (member 6 9)))
>   T
> That seems worse than the old behavior, where the pre-ANSI code
> refused to accept (COMPLEX (MEMBER ...)) types at all. I'd rather have
> code that signals an error about its nonconformance than code which
> quietly gets the wrong answer.

I'm sure that you're right, but I don't see immediately what's wrong
with these -- at least, if I believe sbcl-0.6.13's
UPGRADED-COMPLEX-PART-TYPE.

From the CLHS:

  (complex type-specifier) refers to all complexes that can result
  from giving numbers of type type-specifier to the function complex,
  plus all other complexes of the same specialized representation.

So this type refers to the union of types of
(complex 6 6), (complex 6 9), (complex 9 6) and (complex 9 9), and all
other complexes of the same specialized representation. As far as I
can tell from the sbcl sources, that specialized representation is
(complex rational); upgraded-complex-part-type agrees:

* (upgraded-complex-part-type '(integer 6 6))

RATIONAL
* (upgraded-complex-part-type 'fixnum)

RATIONAL

So, (typep (complex 1/2 3/2) '(complex (member 6 9))) should indeed
give T, by my reading.

Am I wrong?

Christophe

PS: Note that it's entirely possible that I am either missing
something blindingly obvious or that there is something else wrong
with the patch (apart from the NULL/NIL confusion which I hope you
remember about...)
-- 
Jesus College, Cambridge, CB5 8BL                           +44 1223 510 299
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