Re: Remarks on SWI 7

On 29/11/2013, at 4:36 AM, Ulrich Neumerkel wrote:
> Can we agree the Quintus manual differs?
> 
> http://quintus.sics.se/isl/quintus/html/quintus/mpg-ref-length.html

We can agree that the manual doesn't say that there is an
exception if the List argument is malformed, BUT it's arguably
vague.  The whole of the text talks only about what happens
when it is a list (possibly of indefinite length).  It's not
*obvious* what would happen for length(42, 2).

This is actually one of the reasons why a standard scrutinised
by a legion of nitpickers is so useful.  "Things that go without
saying" sometimes need saying, so that everyone says the same.
> 
> It is not part of core, that is ISO/IEC 13211-1, but of the Prolog
> prologue.
> 
> http://www.complang.tuwien.ac.at/ulrich/iso-prolog/prologue

I have *got* to make sure that the pllib.htm document agrees with that.
Remind me.
> 
> There have been discussions on it - primarily Lexington and with
> unanimous agreement and quite numerours participation, we agreed on no
> error for the first argument.

I can argue either way on this one, and I can live with either
outcome.  I *would* be happy with a change; I *am* happy with
what the standard says.

What I was trying to say was that I have strong sympathy with
Jan's preference for length/2 BUT if he's right, _everyone_ should
do the same, and he'd do more good for the world by
 (a) conforming to the standard
 (b) adding a new operation list_length(List, Length) doing what
     he wants
 (c) then lobbying for either the adoption of list_length/2
     or a revision to length/2.