[Maxima] Void in Maxima

Stavros Macrakis macrakis at alum.mit.edu
Sun Oct 4 21:56:34 CDT 2009

```Having some sort of non-printing "void" value is of course doable.

Presumably the main value of such a thing would be for calculations that
really have no result.  OK, a nice little convenience.  Then we'd have to
define the meaning of this thing when combined with other things.  What is
%void+1? %void/%void? if %void then 1 else 0? length(%void), f(%void), etc.
And then implement all those things -- remember, Maxima internally is not
object-oriented in the sense that every operation on a type of object is
centralized under the type definition.  All doable, but a bunch of work.  It
doesn't seem worth it to me, but perhaps there is an argument for it.

A *completely different* topic is non-numerical but perfectly meaningful
values such as inf. limit(x^-2,x,0) really is inf.  It is not undefined, it
is not an error; it is inf.  Yes, I know, in the usual presentations of
calculus, inf is not a value, but a notation.  But Maxima doesn't follow the
usual presentation..... Und and ind, similarly, are not the usual
mathematical conventions for dealing with things like limit(tan(x),x,inf)
and limit(sin(x),x,inf) -- but they are perfectly reasonable conventions,
and again not errors, and not null values.

And how exactly would %void "handle all of the problems with 'und..."?  It
sounds like it would do it simply by replacing them with "problems with
%void"...!

-s

On Sun, Oct 4, 2009 at 10:06 PM, Richard Hennessy <rich.hennessy at verizon.net
> wrote:

>  What about the possibility of creating a new system variable called void
> or %void that would have the properties that I described.  I think this is
> desirable because many times I think a function should not return a value
> when the function fails at its job.  This might be a way to resolve how to
> handle all of the problems with 'und, 'ind, 'inf and 'minf.
>
> Rich
>
>
> ----- Original Message -----
> *From:* Stavros Macrakis <macrakis at alum.mit.edu>
> *To:* Richard Hennessy <rich.hennessy at verizon.net>
> *Cc:* Maxima List <maxima at math.utexas.edu>
> *Sent:* Sunday, October 04, 2009 11:00 AM
> *Subject:* Re: [Maxima] Void in Maxima
>
> On Sun, Oct 4, 2009 at 9:09 AM, Richard Hennessy <
> rich.hennessy at verizon.net> wrote:
>
>> Is there a way to cause a function to have no return value.
>>
>
> No.
>
> It is possible to create a symbol of length 0 using ?intern("\$") which has
> a zero-length printed form, but this has none of the properties you want.
>
>          -s
>
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