Re: Predicate for true lists

[Paul Eggert <eggert@cs.ucla.edu>]

Eli Zaretskii wrote:
> LGTM, pushed.

I don't see why the change is needed; on the contrary, it is counterproductive.

The documentation for "*" doesn't say that "*" signals an error if an argument 
is not a number or a marker; it says only that its arguments are numbers or 
markers. This wording means that if we later extend "*" (say, to support 
multiplication on vectors of numbers), we won't be making an incompatible change.

Similarly, the documentation for "length" need not and should not say that it 
signals an error if its argument is not a sequence; it should merely say that 
its argument is a sequence. Otherwise, we'll be precluding future changes from 
being compatible with the existing documentation.

If we document that "length" signals an error if its argument is the wrong type, 
for consistency shouldn't we have similar documentation for "*" and all other 
functions that signal errors for wrong-type arguments? That sounds like a lot of 
verbiage to add the manual, and its added length would be a cost that would 
exceed any benefit.

Also, I still don't understand why this documentation change would be helpful 
for the proposed proper-list-p implementation. As Eli has acknowledged, the 
proposed implementation does not depend on 'length' signaling an error when 
given a non-sequence. So why is this documentation change needed even for this 
particulare case?