Re: [Info-gnuprologjava] problems running a simple quicksort example

[Daniel Thomas]

Hello,

That error implies that at some point your prolog code is trying to
compare a variable which fails as a variable does not evaluate hence the
instantiation error.

I put:
:- 1 < 2.
:- X = 1, Y = 2, X < Y, Y > X, write(success).
at the end of quicksort.pl to check that < and > are working correctly
and it indicates that they are.

Daniel

On Fri, 2010-11-12 at 13:45 +0100, Benjamin Brunzel wrote:
> Hi,
> 
> Thanks for your answer. As you mentioned there was a bug in the prolog
> rules.
> In line 1 of the prolog file quicksort(A,A). just returns the given
> list. which is obviously wrong.
> I corrected this and now it throws the exception described by me in the
> last mail.
> 
> /usr/lib/jvm/java-6-sun/bin/java -cp
> '/tmp/test/gnuprologjava-0.2.5.jar:.' Test
> ergebnis
> Exception in thread "main" gnu.prolog.vm.PrologException:
> error(instantiation_error,error)
>         at gnu.prolog.vm.PrologException.getError(PrologException.java:129)
>         at gnu.prolog.vm.PrologException.getError(PrologException.java:118)
>         at
> gnu.prolog.vm.PrologException.instantiationError(PrologException.java:145)
>         at gnu.prolog.vm.Evaluate.evaluate(Evaluate.java:153)
>         at
> gnu.prolog.vm.buildins.arithmetics.Predicate_less_than.execute(Predicate_less_than.java:38)
>         at
> gnu.prolog.vm.interpreter.InterpretedByteCode.execute(InterpretedByteCode.java:522)
>         at
> gnu.prolog.vm.interpreter.InterpretedByteCode.execute(InterpretedByteCode.java:522)
>         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)
>         at Test.main(Test.java:37)
> 
> the fixed prolog file is:
> 
> quicksort([],[]).
> quicksort([Kopf|Rest], SortierteListe):- teilen(Kopf, Rest, Kleiner,
> Groesser),quicksort(Kleiner, Kleiner_Sortiert),quicksort(Groesser,
> Groesser_Sortiert),append(Kleiner_Sortiert, [Kopf|Groesser_Sortiert],
> SortierteListe).
> teilen(_, [], [], []).
> teilen(Element, [Kopf|Rest], [Kopf|Kleiner], Groesser):-Kopf < Element,
> !,teilen(Element, Rest, Kleiner, Groesser).
> teilen(Element, [Kopf|Rest], Kleiner, [Kopf|Groesser]):-teilen(Element,
> Rest, Kleiner, Groesser).
> 
> I think the error is related to the less than.
> Prolog programs not using relations like greater than, less than, equal,
> ... seem to work.
> Do you know that error? Do you know a solution to that issue?
> 
> Thanks,
> Ben
> 
> 
> 
> On 11/11/2010 07:54 PM, Daniel Thomas wrote:
> > Hello,
> > I have tried running your code on my machine and the results were as
> > follows:
> >
> > address@hidden:~$ vim Test.java #I removed the line numbers and edited the 
> > path to quicksort.pl
> > address@hidden:~$ vim quicksort.pl
> > address@hidden:~$ javac -cp 
> > '/home/daniel/dev/gnuprolog/releases/0.2.5/gnuprologjava-0.2.5/gnuprologjava-0.2.5.jar'
> >  Test.java
> > address@hidden:~$ java -cp 
> > '/home/daniel/dev/gnuprolog/releases/0.2.5/gnuprologjava-0.2.5/gnuprologjava-0.2.5.jar:.'
> >  Test
> > ergebnis
> > 0
> > .(5,8,1,7,3)
> >
> >
> > What exception do you get? I think that ".(5,8,1,7,3)" is probably the
> > wrong answer as it doesn't appear to be particularly sorted.
> >
> > There is one bug I have found in your prolog:
> > teilen(Element, [Kopf|Rset], Kleiner, [Kopf|Groesser]):-teilen(Element,
> >         Rest, Kleiner, Groesser).
> > "[Kopf|Rset]" should probably be "[Kopf|Rest]"
> >
> > That doesn't fix the missorting though.
> >
> > Does this help you? There is a demo program in the demo directory of the
> > release zip file.
> >
> > In 0.3.0 the return codes of Interpreter.execute(Goal) etc. will be
> > changed to be an enum which will make System.out.println(rc); print
> > something slightly more useful than 0;
> >
> >
> > Daniel
> >
> > On Wed, 2010-11-10 at 14:51 +0100, Benjamin Martin Brunzel wrote:
> >   
> >> Hi Folks,
> >>
> >> I am currently trying to run a simple quicksort example using gnu prolog
> >> for java. I get an exception every time I  use a prolog file with more
> >> then one rule in it.
> >> I think the problem might be the representation of lists in a CompoundTerm
> >> object.
> >> Does anyone know what is wrong with it?
> >> Is there a simple example program available?
> >>
> >> The Java Class:
> >>
> >>   1 import gnu.prolog.term.*;
> >>   2 import gnu.prolog.vm.Environment;
> >>   3 import gnu.prolog.vm.Interpreter;
> >>   4 import gnu.prolog.vm.PrologException;
> >>   5
> >>   6
> >>   7 public class Test {
> >>   8
> >>   9         /**
> >>  10          * @param args
> >>  11          * @throws PrologException
> >>  12          */
> >>  13         public static void main(String[] args) throws PrologException {
> >>  14
> >>  15                 Environment e = new Environment();
> >>  16                
> >> e.ensureLoaded(AtomTerm.get("C:\\Path\\to\\prolog\\files\\quicksort.pl"));
> >>  17                 Interpreter i = e.createInterpreter();
> >>  18                 e.runInitialization(i);
> >>  19
> >>  20                 VariableTerm ergebnis = new VariableTerm("ergebnis");
> >>  21                 IntegerTerm[] elemente = new IntegerTerm[5];
> >>  22                 elemente[0] = new IntegerTerm(5);
> >>  23                 elemente[1] = new IntegerTerm(8);
> >>  24                 elemente[2] = new IntegerTerm(1);
> >>  25                 elemente[3] = new IntegerTerm(7);
> >>  26                 elemente[4] = new IntegerTerm(3);
> >>  27
> >>  28                 CompoundTerm liste = new CompoundTerm(".", elemente);
> >>  29
> >>  30                 Term[] argumente = {ergebnis, liste};
> >>  31
> >>  32                 CompoundTerm anfrage = new CompoundTerm("quicksort",
> >> argumente);
> >>  33
> >>  34                 System.out.println(ergebnis);
> >>  35
> >>  36                 Interpreter.Goal goal = i.prepareGoal(anfrage);
> >>  37                 int rc = i.execute(goal);
> >>  38                 System.out.println(rc);
> >>  39
> >>  40                 System.out.println(ergebnis);
> >>  41
> >>  42         }
> >>  43
> >>  44 }
> >>
> >> The Prolog File:
> >>
> >> quicksort(A, A).
> >> quicksort([Kopf|Rest], SortierteListe):- teilen(Kopf, Rest, Kleiner,
> >> Groesser),quicksort(Kleiner, Kleiner_Sortiert),quicksort(Groesser,
> >> Groesser_Sortiert),append(Kleiner_Sortiert    , [Kopf|Groesser_Sortiert],
> >> SortierteListe).
> >> teilen(_, [], [], []).
> >> teilen(Element, [Kopf|Rest], [Kopf|Kleiner], Groesser):-Kopf < Element,
> >> !,teilen(Element, Rest, Kleiner, Groesser).
> >> teilen(Element, [Kopf|Rset], Kleiner, [Kopf|Groesser]):-teilen(Element,
> >> Rest, Kleiner, Groesser).
> >>
> >>
> >> I used the version 0.2.5
> >>
> >> Please note that I am not on the mailing list so please cc me on your
> >> answers.
> >>
> >> Thanks for your support.
> >>
> >>
> >>
> >>     
> >   
>

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