🚀 go-pugleaf

In article <1992Aug26.130909.17909@neptune.inf.ethz.ch> marti@nugget.inf.ethz.ch (Robert Marti) writes:
>In article <1992Aug25.074623.25450@greco-prog.fr>, billaud@greco-prog.fr
>(Michel BILLAUD) writes:
>|> In article <meskes.713709771@ulysses>
>|> meskes@ulysses.informatik.rwth-aachen.de (Michael Meskes) writes:
>|> 
>|> > Can you program a IF...THEN...ELSE in Prolog without using the cut?
>|> 
>|> No. a proof by contradiction:
>
>[ proof deleted ]
>
>I am sorry to contradict your contradiction ;-)  As someone else has
>pointed out, it _is_ possible to program if-then-else without cut
>IN CERTAIN SPECIAL CASES.

Yes (I'm happy to agree :-)), it's possible in certain special cases *only*.
The [deleted] result was about the impossibility to build a *general* 
IF-THEN-ELSE construct from AND/OR/TRUE/FAIL, so where's the contradiction?

Also, it's possible to replace cut by if-then-else in a number of cases
(clauses with no ";"), but not in *all* the cases. for example, try:
	p(X) :-  g(X), ((r(X),!,fail);true).

Michel


-- 
Michel BILLAUD                 :  billaud@geocub.greco-prog.fr
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