Re: Dave Plummer's bagof query

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1 total messages Started by Chris Moss Fri, 22 Aug 1986 09:53

#746

Author: Chris Moss
Date: Fri, 22 Aug 1986 09:53

33 lines
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>>Date: Wed 6 Aug 86 14:38:43-CDT
>>From: Dave Plummer <ATP.PLUMMER@R20.UTEXAS.EDU>
>>Subject: DEC-10 Bagof - Bug?
>>
>>Given the program:
>>
>>p(1,_). p(2,_). p(3,3). p(4,4).
>>
>>and the goal bagof(X, p(X,Y), S).  Edinburgh DEC-10 Prolog
>>returns,
>>
>>S = [1,2,3] X = _ Y = 3
>>S = [4]     X = _ Y = 4
>>
>>This behaviour doesn't agree with my reading of the
>>documentation

Poplog produces the solutions:
	S=[4]  X =_1 Y=4
	S=[3]  X =_1 Y=3
	S=[1,2] X=_1 Y=_2

which is _slightly_ more consistent.
The problem has been dealt with in:
  Lee Naish: All solutions predicates in Prolog.
	Tech Report 84/4, Dept of Comp. Sc., Univ of Melbourne.
(it's been published I think, but I forget where)
He has a 'hard-line' solution which involves coroutining and
never returning variables if they can be subsequently bound.

Chris Moss.  cdsm@doc.ic.ac.uk cdsm@icdoc.uucp

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