🚀 go-pugleaf

In article <3470@geocub.UUCP>, billaud@geocub.UUCP (Michel BILLAUD)
QUOTES

> What about:
> 
> 5. If b is deterministic and followed by a !, you can switch them:
>      p :- a,...,b,!,c,...     
>      p :- a,...,!,b,c,...

This is false.  Consider
	p :- fail, !.				p :- !, fail.
	p :- write(yoo-hoo).			p :- write(yoo-hoo).
	?- p.					?- p.
    =>	yoo-hoo				    =>	no
If b is determinate (not "deterministic") and cannot fail, _then_ you
can switch them.


> From csa09@seq1.keele.ac.uk Mon May 27 12:04:26 1991
> From: "P." Singleton <csa09@seq1.keele.ac.uk>

> If a (deterministic) goal doesn't instantiate its arguments 
> any further (perhaps it has useful side-effects), then you 
> can replace it by
> 
> 	\+ \+ goal

The DEC-10 Prolog library defines gcc(G) :- \+ \+ X.
It stands for "garbage collecting call".

> Nota : \+ = not

Note:  in DEC-10 Prolog and Quintus Prolog 'not' is _not_ the same
as "unprovable" \+ .  In both Prologs, 'not' is not an evaluable
predicate, but is defined in the library, and is defined to report
an error when it won't be sound.  Stick with \+ for portability.
-- 
I agree with Jim Giles about many of the deficiencies of present UNIX.