Re: negotiation by failure- list operations

Brian Hulley wrote:

However "yes" and "no" is just due to the vagaries of the top level and
shouldn't really be bothered about all that much.


Ah ! Finally a relevant point in this exchange of vagaries :-)
(and why did nobody point out that there is no throwing involved in
the Yes or No ? are you really relying on me to *** in :-?)

The toplevel behaviour is not defined by ISO (it is considered
"environmental") - the toplevel query ?- X = 1. can result in

	immediate yes and no alternatives prompt (GNU)
	immediate yes with an alternatives prompt
	neither yes nor no, but with an alternatives prompt (SICStus,
			SWI, Yap ...)
		and the yes or no comes after you type <CR> or ;<CR>
	...

And sometimes the behaviour depends on whether the query is ground or
not - all very ad hoc and unnecessarily confusing to the beginner (and
sometimes to the old hogs as well). Sure, there are historc reasons for
some of these, but maybe it is time Prolog implementors get rid of bad
memories ?

Cheers

Bart Demoen
.