Re: [Info-gnuprologjava] problem creating queries with NOT (negation as failure)

[Daniel Thomas]

Hello,

Sorry for the long delay in getting back to you about this.

From: ISO/IEC CD 13211-1 : 1996(E)

8.15.1 fail_if/1

NOTE — A predicate with the same meaning as fail_if/1 is
implemented in many existing processors with a name not/1
which is misleading because the predicate gives negation by
failure rather than true negation. Other processors implement
this feature with a predicate \+/1.

Unfortunately it looks like GPJ does not provide the not/1 predicate and
that there is some misleading bug in runOnce where the wrong error
message can be shown (probably due to the finally being used for
clearup) and so the actual error message:
gnu.prolog.vm.PrologException: error(existence_error(procedure,not / 1),error)
        at gnu.prolog.vm.PrologException.getError(PrologException.java:129)
        at gnu.prolog.vm.PrologException.getError(PrologException.java:118)
        at 
gnu.prolog.vm.PrologException.existenceError(PrologException.java:155)
        at 
gnu.prolog.vm.UndefinedPredicateCode.execute(UndefinedPredicateCode.java:62)
        at 
gnu.prolog.vm.interpreter.InterpretedByteCode.execute(InterpretedByteCode.java:522)
        at 
gnu.prolog.vm.interpreter.Predicate_call.staticExecute(Predicate_call.java:144)
        at gnu.prolog.vm.Interpreter.execute(Interpreter.java:507)

gets hidden.

It also appears that GPJ does not provide fail_if, which is also an
error, we should probably support both fail_if/1 and not/1. In the
meantime you can trivially define them in terms of \+/1 and include that
in a file you ensureLoaded or define that from within GPJ in java.

Sorry for the delay in replying.

Daniel

On Fri, 2012-04-27 at 17:12 +0530, Suman Roy wrote:
> We are using gnuprolog 0.2.5 to create queries to fire onto Prolog.
> 
>  
> 
> We are unable to create queries which involve NOT as negation as
> failure like, "not( bird (cat) )". 
> 
> In order to form such query we tried implementing in the way as you
> mentioned previously .
> 
>  
> 
> Here is the code snippet  : 
> 
> ------------------
> 
>  
> 
>           Term t1[] = {  AtomTerm.get ( " cat " )  } ; 
> 
>  
> 
>    CompoundTerm ct1=new CompoundTerm ( " bird ", t1 ) ;
> 
>  
> 
>    CompoundTerm goalTerm=new
> CompoundTerm(CompoundTermTag.get("not",1),ct1);
> 
>  
> 
>             int rc = in.runOnce(goalTerm);
> 
>  
> 
> But we are getting a Java Exception :  “  Exception in thread "main"
> java.lang.IllegalArgumentException: The goal is not currently active
> ” .
> 
>  
> 
> Can anybody please provide some help? We need this urgently.
> 
>  
> 
> Suman Roy, Ph.D.
> Infosys LABS, 
> 
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