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

[Daniel Thomas]

Hello,

> echo "quicksort([H|T],T)." >> quicksort.pl
This shouldn't unify. It means "sort the list of H as the beginning of
the list which continues with T and obtain the list T" i.e. sort a list
and get a shorter list which should not happen.

> Is it possible to use the [Head|Tail] notation in  gnu prolog for java?
Yes.

> Is our list representation in the java file correct?
No. Lists consist of .(A,.(B,.(C,[]))) rather than .(A,B,C,[]) which is
what your code means.
You want to use: 
CompoundTerm list = CompoundTerm.getList(elements);

> Do you know what might be the problem?
I suspect that is the problem.

I hope that helps,

Daniel

On Fri, 2010-11-19 at 13:02 +0100, Benjamin Brunzel wrote:
> Hi,
> 
> Thanks again for your efforts. We found our mistake in our java file.
> But it seems like there is another thing preventing us from running our
> prolog quicksort.
> We made some tests and it looks like there is a problem with our list
> representation
> in the java program.
> We tried to run a simple single list rule in the prolog that looks like
> this:
> 
> echo "quicksort([H|T],T)." >> quicksort.pl
> 
> Running this with our java file we get a return value of -1 which
> implies that there
> was no unification taking place.
> 
> Is it possible to use the [Head|Tail] notation in  gnu prolog for java?
> Is our list representation in the java file correct?
> Do you know what might be the problem?
> 
> Best regards,
> Ben
> 
> 
> The current Java File:
> 
> import gnu.prolog.term.*;
> import gnu.prolog.vm.Environment;
> import gnu.prolog.vm.Interpreter;
> import gnu.prolog.vm.PrologException;
>  
> 
> public class Test {
>     public static void main(String[] args) throws PrologException {
>         //initialisation
>         Environment e = new Environment();
>         e.ensureLoaded(AtomTerm.get("quicksort.pl"));
>         Interpreter i = e.createInterpreter();
>         e.runInitialization(i);
>        
>         //definition of the Terms
>         VariableTerm result = new VariableTerm("R");
>          
>         IntegerTerm[] elements = new IntegerTerm[5];
>         elements[0] = new IntegerTerm(5);
>         elements[1] = new IntegerTerm(8);
>         elements[2] = new IntegerTerm(1);
>         elements[3] = new IntegerTerm(7);
>         elements[4] = new IntegerTerm(3);
> 
>         // defining the list
>         CompoundTerm list = new CompoundTerm(".", elements);
>  
>         Term[] arguments = {list, result};       
>         //composing the request
>         CompoundTerm request = new CompoundTerm("quicksort", arguments);
>          
>         System.out.println(result);
>                
>         //execute the request
>         Interpreter.Goal goal = i.prepareGoal(request);
>         int rc = i.execute(goal);
>         //printing results
>         System.out.println(rc);
>         System.out.println(result);         
>     }
> }
> 
> 
> On 11/13/2010 04:49 PM, Daniel Thomas wrote:
> > 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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