Is.java

package org.archstudio.prolog.op.iso;

import java.util.Collections;
import java.util.List;
import java.util.Map;

import org.archstudio.prolog.engine.PrologUtils;
import org.archstudio.prolog.engine.ProofContext;
import org.archstudio.prolog.engine.UnificationContext;
import org.archstudio.prolog.engine.UnificationEngine;
import org.archstudio.prolog.op.Executable;
import org.archstudio.prolog.term.ComplexTerm;
import org.archstudio.prolog.term.ConstantTerm;
import org.archstudio.prolog.term.Term;
import org.archstudio.prolog.term.VariableTerm;

public class Is extends ComplexTerm implements Executable {

	public Is(String name, List<? extends Term> terms) {
		super(name, 2, terms);
	}

	@Override
	public Iterable<Map<VariableTerm, Term>> execute(ProofContext proofContext, UnificationEngine unificationEngine,
			Term source, Map<VariableTerm, Term> variables) {
		UnificationContext context = new UnificationContext(proofContext, getTerm(0), new ConstantTerm(
				PrologUtils.evaluate(proofContext, getTerm(1), variables)), variables);
		if (unificationEngine.unifies(proofContext, context)) {
			return Collections.singleton(context.variables);
		}
		return Collections.emptyList();
	}
}