Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!zodiac!DEIMOS.ADS.COM!rar
From: rar@DEIMOS.ADS.COM (Bob Riemenschneider)
Newsgroups: comp.lang.prolog
Subject: existential quantification in bagof and setof
Message-ID: <8902072057.AA21884@deimos.ads.com>
Date: 7 Feb 89 20:57:03 GMT
Sender: daemon@zodiac.UUCP
Lines: 33

=>   E.g., given the DB
=>
=>   foo(1,2,3,4).
=>   foo(2,3,4,5).
=>   foo(3,4,5,6).
=>   foo(4,5,6,7).
=>
=>   I can do
=>
=>   | ?- T = p(X,Y,Z), setof(First, T^foo(First,X,Y,Z), Set).
=>
=>   T = p(X,Y,Z),
=>   X = _79,
=>   Y = _94,
=>   Z = _109,
=>   First = _132,
=>   Set = [1,2,3,4] 
=>
=>   I'd be curious to find out if other Prologs work like this.

I tried this in AAIS Prolog version M-1.15 on my Mac and got:

   ?-  T = p(X,Y,Z), setof(First, T^foo(First,X,Y,Z), Set).
         T = p(2,3,4),
         X = 2, Y = 3, Z = 4, First = _4, Set = [1] ;
         T = p(3,4,5),
         X = 3, Y = 4, Z = 5, First = _4, Set = [2] ;
           ...

According to the AAIS manual, the "goal [VAR^GOAL] is equivalent
to just calling GOAL if the variable [VAR] is bound."

							-- rar