Re: [Reduce-algebra-developers] Use of t and nil in Reduce

[Arthur N. <ac...@ca...>]

If you switch "on comp" so that CSL compiles things I believe you will see 
diagnostics (albeit not very nice ones) from your first two cases.
At the Lisp level it can not make sense to refuse to allow "e", "i" etc to 
be local variables, or else
   for i := 1:n do ...
would be rejected and MANY people would be upset.

The symbols "nil" and "t" have special historical meanings at the level of 
symbolic (lisp level) code and maybe for them "form" and friends could 
rename them to something anodyne if seen in algebraic-level code so that 
for ordinary algebraic users they would not be reserved any more. That MAY 
be as easy as addint to the algid procedure in rlisp/form.red
   if u = nil then 'algebraic!:nil
   else if u = t then 'algebraic!:t
   else whatever it had before
and in a matching way arranging that printing new to map the internal 
names back to what they were on input.

For e, i, pi and possibly MANY others the most I feel one could do would 
be to consider a warning message. But the "for i := 1:n" example is close 
to enough to persuade me that even that will hurt at least as many people 
as it helps.

Arthur


On Thu, 20 Oct 2011, Rainer Schöpf wrote:

> The recent bug report
>
>  https://sourceforge.net/tracker/?func=detail&atid=1126256&aid=3426364&group_id=248416
>
> made me test how t and nil behave in algebraic mode. Try the following:
>
> algebraic procedure x(t); t;
> algebraic procedure y(nil); nil;
> algebraic procedure z(e);e;
> x(1);
> y(1);
> z(1);
>
> CSL returns 1 in all cases, PSL replies with
>
> ***** T and NIL cannot be rebound
>
> in the first two.
>
> I think the use of reserved identifiers as formal parameters or free variables
> in a rule should lead to an error.
>
>    Rainer
>
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