[JENA-489] error message for builtin with wrong number of args is wrong

• Type: Bug
• Status: Closed
• Priority: Trivial
• Resolution: Fixed
• Affects Version/s: Jena 2.10.0
• Fix Version/s: Jena 2.11.0
• Component/s: Jena
• Assignee: Andy Seaborne
• Reporter: Joshua Taylor
• Created: 17/Jul/13 20:06
• Updated: 21/Jul/13 16:54
• Resolved: 21/Jul/13 16:54

Description

The message for a syntax error in the rule parser when a builtin is used in a backwards rule with the wrong number of arguments is wrong. The message is generated in emitBody(Functor functor) in RuleClauseCode by these lines:

                throw new LPRuleSyntaxException("Wrong number of arguments to functor " + functor.getName() 
                                                  + " expected " + functor.getArgLength(), rule);

Instead of functor.getArgLength() should be builtin.getArgLength(). In context these are:

        void emitBody(Functor functor) {
            Node[] fargs = functor.getArgs();
            Builtin builtin = functor.getImplementor();
            if (builtin == null) {
                throw new LPRuleSyntaxException("Unknown builtin operation " + functor.getName(), rule);
            }
            if (builtin.getArgLength() != 0 && builtin.getArgLength() != fargs.length) {
                throw new LPRuleSyntaxException("Wrong number of arguments to functor " + functor.getName() 
                                                  + " expected " + functor.getArgLength(), rule);
            }
            for (int i = 0; i < fargs.length; i++) {
                Node node = fargs[i];
                // We optionally force an eager dereference of variables here.
                // We used to force this but the current builtin implementations
                // now robust against it (the do a deref themselves anyway).
                 emitBodyPut(node, i, true);
            }
            code[p++] = CALL_BUILTIN;
            code[p++] = (byte)fargs.length;
            args.add(builtin);
        }

Code that demonstates the misleading message follows:

import com.hp.hpl.jena.rdf.model.InfModel;
import com.hp.hpl.jena.rdf.model.Model;
import com.hp.hpl.jena.rdf.model.ModelFactory;
import com.hp.hpl.jena.reasoner.rulesys.GenericRuleReasoner;
import com.hp.hpl.jena.reasoner.rulesys.Rule;
import com.hp.hpl.jena.reasoner.rulesys.builtins.Sum;
import com.hp.hpl.jena.vocabulary.RDF;

public class JenaBuiltinErrorMessageExample {
	static String rules = "" +
			"[(?x thriceValue ?vvv) <-\n" +
			" (?x rdf:value ?v)\n" +
			" sum(?v,?v,?v,?vvv)]\n" +
			"";
	Sum sum;
	public static void main( String[] args ) {
		GenericRuleReasoner reasoner = new GenericRuleReasoner( Rule.parseRules( rules ));
		Model base = ModelFactory.createDefaultModel();
		base.createResource().addLiteral( RDF.value, 10 );
		InfModel inf = ModelFactory.createInfModel( reasoner, base );
		inf.write( System.out, "N3" );
	}
}

This throws an exception with a misleading message:

Exception in thread "main" com.hp.hpl.jena.reasoner.rulesys.impl.LPRuleSyntaxException: Syntax error in backward rule: [ (?x thriceValue ?vvv) <- (?x rdf:value ?v) sum(?v ?v ?v ?vvv) ]
Wrong number of arguments to functor sum expected 4
	at com.hp.hpl.jena.reasoner.rulesys.impl.RuleClauseCode$CompileState.emitBody(RuleClauseCode.java:607)
	at com.hp.hpl.jena.reasoner.rulesys.impl.RuleClauseCode.compile(RuleClauseCode.java:213)
	at com.hp.hpl.jena.reasoner.rulesys.impl.LPRuleStore.compileAll(LPRuleStore.java:249)
	at com.hp.hpl.jena.reasoner.rulesys.impl.LPRuleStore.codeFor(LPRuleStore.java:99)
	at com.hp.hpl.jena.reasoner.rulesys.impl.LPRuleStore.codeFor(LPRuleStore.java:119)
	at com.hp.hpl.jena.reasoner.rulesys.impl.LPInterpreter.<init>(LPInterpreter.java:91)
	at com.hp.hpl.jena.reasoner.rulesys.impl.LPBRuleEngine.find(LPBRuleEngine.java:109)
	at com.hp.hpl.jena.reasoner.rulesys.FBRuleInfGraph.findWithContinuation(FBRuleInfGraph.java:575)
	at com.hp.hpl.jena.reasoner.rulesys.FBRuleInfGraph.graphBaseFind(FBRuleInfGraph.java:606)
	at com.hp.hpl.jena.reasoner.BaseInfGraph.graphBaseFind(BaseInfGraph.java:370)
	at com.hp.hpl.jena.graph.impl.GraphBase.find(GraphBase.java:266)
	at com.hp.hpl.jena.graph.compose.DisjointUnion.graphBaseFind(DisjointUnion.java:39)
	at com.hp.hpl.jena.graph.impl.GraphBase.find(GraphBase.java:266)
	at com.hp.hpl.jena.graph.impl.GraphBase.graphBaseFind(GraphBase.java:287)
	at com.hp.hpl.jena.graph.impl.GraphBase.find(GraphBase.java:284)
	at com.hp.hpl.jena.rdf.model.impl.ModelCom.listStatements(ModelCom.java:449)
	at com.hp.hpl.jena.rdf.model.impl.ModelCom.listStatements(ModelCom.java:455)
	at com.hp.hpl.jena.n3.N3JenaWriterPP.prepareLists(N3JenaWriterPP.java:81)
	at com.hp.hpl.jena.n3.N3JenaWriterPP.prepare(N3JenaWriterPP.java:67)
	at com.hp.hpl.jena.n3.N3JenaWriterCommon.processModel(N3JenaWriterCommon.java:275)
	at com.hp.hpl.jena.n3.N3JenaWriterCommon.write(N3JenaWriterCommon.java:197)
	at com.hp.hpl.jena.n3.N3JenaWriterCommon.write(N3JenaWriterCommon.java:209)
	at com.hp.hpl.jena.n3.N3JenaWriter.write(N3JenaWriter.java:171)
	at com.hp.hpl.jena.rdf.model.impl.ModelCom.write(ModelCom.java:327)
	at JenaBuiltinErrorMessageExample.main(JenaBuiltinErrorMessageExample.java:20)