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    <p>I'm going insane with this...</p> <p>As I already mentioned above, there are some differences between Prolog in Java and Prolog via SWI.</p> <p>I'm currently using this code:</p> <pre><code>% this data is from original Prolog Dijkstra' algorithm implementation :- dynamic(best_so_far/2). findPath([Goal | Rest], Goal, Temp, Temp, [Goal | Rest]) :- !. findPath([A | Rest], Goal, Cost, Temp, Path) :- path(A, B, C), \+ member(B, Rest), NewCost is Temp + C, best_so_far(Limit, _), NewCost &lt; Limit, findPath([B, A | Rest], Goal, Cost, NewCost, Path). % ?- searchPath(aberdeen, glasgow, L, P). % searchPath(Start, Goal, BestLen, BestPath) :- retract_all(best_so_far(_, _)), asserta(best_so_far(50, [])), findPath([Start], Goal, Cost, 0, Path), % if we get here, it's because a lower Cost exists retract_all(best_so_far(_,_)), asserta(best_so_far(Cost, Path)), fail ; best_so_far(BestLen, BestPath). retract_all(Term):- retract(Term),fail. retract_all(_). </code></pre> <p>Asking for a result in SWI Prolog I'll get an answer in <strong>0.016 seconds</strong>. Java needs <strong>15 seconds</strong> for the same result! </p> <p><strong>Furthermore and even worse:</strong> at some point gnu prolog delivers <strong>a completely different result</strong>.</p> <p>Here is some outline of Java:</p> <pre><code>From 190 to 221 pathList: [221, 191, 190] distance: 2 From 191 to 221 pathList: [221, 251, 252, 253, 223, 193, 194, 195, 196, 197, 198, 199, 169, 139, 138, 137, 136, 135, 134, 133, 132, 131, 130, 129, 128, 127, 126, 125, 124, 123, 122, 121, 151, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191] distance: 43 From 190 to 221 pathList: [221, 191, 190] distance: 2 </code></pre> <p>You can clearly see, that there is a path from <strong>191</strong> to <strong>221</strong>. But instead of returning this result (<code>pathList: [221,191]</code>) I get a competely different path leading backwards from where my ghost came. Running the Query <code>searchPath(191,221, Distance, Path)</code> in SWI Prolog (instantly) returns </p> <pre><code>7 ?- searchPath(191,221, Cost, Path). Cost = 1, Path = [221, 191]. </code></pre> <p>Once again: I'm using the exact same code. I Copy&amp;Pasted it to make sure. And I'm passing the correct arguments (that's why I print them out).</p> <p><strong>I really don't know how to thank you (especially CapelliC). I'm sure you already spent far too much time for me. But I'm definitely on my wits' end.</strong></p> <p>Edit: Thought it might be useful to see my java code:</p> <pre><code>private int decideHunterMovement() { // term which contains the result of the prolog method VariableTerm pathTerm = new VariableTerm("Path"); VariableTerm distanceTerm = new VariableTerm("Distance"); Integer movement; List&lt;IntegerTerm&gt; pathList = new LinkedList&lt;IntegerTerm&gt;(); // Create the arguments to the compound term which is the question IntegerTerm hunterPosition = new IntegerTerm(hunter.getPosition()); IntegerTerm targetPosition = new IntegerTerm(pacman.getPosition()); // target for hunter is the pacman position long time= System.nanoTime (); Term[] arguments = { hunterPosition, targetPosition, distanceTerm, pathTerm}; // Construct the question CompoundTerm goalTerm = new CompoundTerm(AtomTerm.get("searchPath"), arguments); // Execute the goal and return the return code. int rc; System.out.println("From " + hunterPosition + " to " + targetPosition); try{ // Create the answer rc = interpreter.runOnce(goalTerm); time = (System.nanoTime () - time) / 1000 / 1000; System.out.println("Result in:" + time+ "ms"); // If it succeeded. if (rc == PrologCode.SUCCESS || rc == PrologCode.SUCCESS_LAST){ // Get hold of the actual Terms which the variable terms point to Term path = pathTerm.dereference(); Term distance = distanceTerm.dereference(); // Check it is valid if (path != null){ if (path instanceof CompoundTerm){ // convert CompoundTerm to a Java LinkedList convertToList((CompoundTerm) path, pathList); if(VERBOSE_MODE){ System.out.println("pathList: " + pathList); System.out.println("distance: " + (IntegerTerm) distance + "\n"); } }else{ throw new NoAnswerException("PROLOG ERROR: Answer is not a CompundTerm: (" + path + ")"); } }else{ throw new NoAnswerException("PROLOG ERROR: Answer null when it should not be null"); } }else{ throw new NoAnswerException("PROLOG ERROR: Goal failed"); } } catch (NoAnswerException e) { e.printStackTrace(); } catch (PrologException e1) { e1.printStackTrace(); } movement = decideMovement(pathList); return movement; } </code></pre>
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    1. POUsing (nb_)setarg/3 with gnu.prolog in Java
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    1. COI finally managed to use JPL from SWI Prolog. With this framework everything works fine...
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    2. COSetup such environment can be a pain, but it's a rewarding step in perspective.
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