[Openmcl-devel] Type-of and positive/negative integers

Steven Nunez steve_nunez at yahoo.com
Thu Oct 24 02:40:21 PDT 2019

 Huh. Interesting. That works, thanks very much. I wouldn't have thought of that. Of course now I have to go figure out why this works...

    On Thursday, October 24, 2019, 4:07:11 PM GMT+8, Daniel Kochmański <daniel at turtleware.eu> wrote:  
 or, alternatively, just use class-of instead of type-of.

Daniel Kochmański writes:

> Hmm, maybe something in this spirit?
> (let ((type (type-of x)))
>  (flet ((maximize-type (new-number)
>            (let ((new-type (type-of new-number)))
>              (cond ((subtypep new-type type)
>                    t)
>                    ((subtypep type new-type)
>                    (setf type new-type)
>                    t)))))
>      (assert (every #'maximize-type coefficients))))
> Daniel
> Steven Nunez writes:
>>  Okay, having a specialised representation for positive integers makes sense as a further specialisation of INTEGER. I wish this was documented somewhere, a 1 minute google search did not turn up anything.
>> I still have the problem of ensuring that the parameters to a function, a sequence and a number, are all of the same type so I can dispatch on specialised (typed declared) versions of loop. At the moment I have:
>>  (assert (and (plusp (length coefficients))
>>    (every (lambda (elt)
>>      (typep elt (type-of x)))
>>    coefficients)))
>> which works fine for single-float and double-float, but fails if any of the coefficients are negative because their type-of is FIXNUM whilst the X or other coefficients may be (INTEGER 0 4611686018427387903)
>> Any ideas?
>>    On Thursday, October 24, 2019, 3:24:56 PM GMT+8, Daniel Kochmański <daniel at turtleware.eu> wrote:  
>>> CCL (1.11) has most-positive-fixnum of 1152921504606846975SBCL (1.5.6) has 4611686018427387903
>>> However:
>>> CL-USER> (subtypep 'fixnum 'integer)
>>> T
>>> T
>>> CL-USER>
>>> so FIXNUM is a subtype of INTEGER, and it should be the type returned if the implementation is following the CltL2 guidelines if I'm understanding the type system correctly.
>> CLtL2 has been superseded by ANSI specification so it is not
>> bounding. Anyway, more specific type here is
>>  (integer 0 #.most-positive-fixnum)
>> Try (subtypep (integer 0 #.most-positive-fixnum) 'fixnum) and it will
>> yield true as well.
>> The reason why you have result 'fixnum for negative and '(integer 0
>> #.most-positive-fixnum) for positive integers is probably because CCL
>> (and other implementations in fact) have a specialized representation
>> for unsinged fixnums (similar to i.e 'unsigned int' in C).
>> Daniel

Daniel Kochmański ;; aka jackdaniel | Przemyśl, Poland
TurtleWare - Daniel Kochmański      | www.turtleware.eu

"Be the change that you wish to see in the world." - Mahatma Gandhi  
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