Re: SWI Prolog forgets identity of query variables in CHR ???

Hello Henning,

What did you expect when queering  ?- c(X,Y). ?

Remember CHR select a constraint by matching the not by unification.
If unification is needed the CHR constraint has to be
	c(X,Animal) <=> Animal = cow | d(X,pig).

Hope this helps

Uwe


> -----Original Message-----
> From: [email protected]
> bonn.de [mailto:swi-prolog-bounces+lesta=sbs-
> [email protected]] On Behalf Of Henning
> Christiansen
> Sent: Tuesday, February 25, 2014 12:43 PM
> To: [email protected]
> Subject: [SWIPL] SWI Prolog forgets identity of query variables in CHR
> ???
> 
> Hi SWIPL team,
> 
> I observed strange problem that the identity of variables in CHR
> queries are sometimes forgotten when the resylt is printed out.
> I could isolate the problem into a one rule program.
> For the two test queries, no rule is applied;
> the first one behaves as you would expect, but in the second one, my
> query variables gets renamed and thus the semantics of the answer is
> wrong.
> 
> If I have a program with no rules, no misbehaviour is observed
> 
> (running on Mac OS 10.9.1)
> 
> best wishes
> 
>      Henning
> 
> 
> The program:
> 
> :- use_module(library(chr)).
> :- chr_constraint c/2, d/2.
> c(X,cow) <=> d(X,pig).
> 
> Queries:
> $ swipl
> Welcome to SWI-Prolog (Multi-threaded, 64 bits, Version 6.6.1-DIRTY)
> ....
> 
> ?- [program].
> %  library(chr) compiled into chr 0.51 sec, 6,504 clauses
> % program compiled 0.51 sec, 6,551 clauses
> true.
> 
> ?- c(X,duck).
> c(X,duck)
> true .
> c(X,duck)
> 
> ?- c(X,Y).
> c(_G30729,_G30730)
> true .
> c(_G30729,_G30730)
> 
> 
> 
> 
> 
> Henning Christiansen
> Professor of  Computer Science, PhD
> Leader of Research group PLIS: Programming, Logic and Intelligent
> Systems
> Department of Communication, Business and Information Technologies
> Roskilde University
> P.O.Box 260, DK-4000 Roskilde, DENMARK
> http://www.ruc.dk/~henning
> 
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