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A modified version of the GGP-Base library for Alloy.
The newest version!
package org.ggp.base.util.gdl;

import java.util.Collection;

import org.ggp.base.util.gdl.grammar.Gdl;
import org.ggp.base.util.gdl.grammar.GdlConstant;
import org.ggp.base.util.gdl.grammar.GdlDistinct;
import org.ggp.base.util.gdl.grammar.GdlFunction;
import org.ggp.base.util.gdl.grammar.GdlLiteral;
import org.ggp.base.util.gdl.grammar.GdlNot;
import org.ggp.base.util.gdl.grammar.GdlOr;
import org.ggp.base.util.gdl.grammar.GdlProposition;
import org.ggp.base.util.gdl.grammar.GdlRelation;
import org.ggp.base.util.gdl.grammar.GdlRule;
import org.ggp.base.util.gdl.grammar.GdlSentence;
import org.ggp.base.util.gdl.grammar.GdlTerm;
import org.ggp.base.util.gdl.grammar.GdlVariable;


public class GdlVisitors {
    /**
     * Visits the given Gdl object and any contained Gdl objects within
     * with the given GdlVisitor. For example, when called on a GdlRule,
     * the visitor's visitConstant function is called once for every
     * constant anywhere in the head or body of the rule.
     *
     * @author Alex Landau
     */
    public static void visitAll(Gdl gdl, GdlVisitor visitor) {
        visitor.visitGdl(gdl);
        if (gdl instanceof GdlTerm) {
            visitTerm((GdlTerm) gdl, visitor);
        } else if (gdl instanceof GdlLiteral) {
            visitLiteral((GdlLiteral) gdl, visitor);
        } else if (gdl instanceof GdlRule) {
            visitRule((GdlRule) gdl, visitor);
        } else {
            throw new RuntimeException("Unexpected Gdl type " + gdl.getClass());
        }
    }
    public static void visitAll(Collection collection, GdlVisitor visitor) {
        for (Gdl gdl : collection) {
            visitAll(gdl, visitor);
        }
    }
    private static void visitRule(GdlRule rule, GdlVisitor visitor) {
        visitor.visitRule(rule);
        visitAll(rule.getHead(), visitor);
        visitAll(rule.getBody(), visitor);
    }
    private static void visitLiteral(GdlLiteral literal, GdlVisitor visitor) {
        visitor.visitLiteral(literal);
        if (literal instanceof GdlSentence) {
            visitSentence((GdlSentence) literal, visitor);
        } else if (literal instanceof GdlNot) {
            visitNot((GdlNot) literal, visitor);
        } else if (literal instanceof GdlOr) {
            visitOr((GdlOr) literal, visitor);
        } else if (literal instanceof GdlDistinct) {
            visitDistinct((GdlDistinct) literal, visitor);
        } else {
            throw new RuntimeException("Unexpected GdlLiteral type " + literal.getClass());
        }
    }
    private static void visitDistinct(GdlDistinct distinct, GdlVisitor visitor) {
        visitor.visitDistinct(distinct);
        visitAll(distinct.getArg1(), visitor);
        visitAll(distinct.getArg2(), visitor);
    }
    private static void visitOr(GdlOr or, GdlVisitor visitor) {
        visitor.visitOr(or);
        for (int i = 0; i < or.arity(); i++) {
            visitAll(or.get(i), visitor);
        }
    }
    private static void visitNot(GdlNot not, GdlVisitor visitor) {
        visitor.visitNot(not);
        visitAll(not.getBody(), visitor);
    }
    private static void visitSentence(GdlSentence sentence, GdlVisitor visitor) {
        visitor.visitSentence(sentence);
        if (sentence instanceof GdlProposition) {
            visitProposition((GdlProposition) sentence, visitor);
        } else if (sentence instanceof GdlRelation) {
            visitRelation((GdlRelation) sentence, visitor);
        } else {
            throw new RuntimeException("Unexpected GdlSentence type " + sentence.getClass());
        }
    }
    private static void visitRelation(GdlRelation relation, GdlVisitor visitor) {
        visitor.visitRelation(relation);
        visitAll(relation.getName(), visitor);
        visitAll(relation.getBody(), visitor);
    }
    private static void visitProposition(GdlProposition proposition,
            GdlVisitor visitor) {
        visitor.visitProposition(proposition);
        visitAll(proposition.getName(), visitor);
    }
    private static void visitTerm(GdlTerm term, GdlVisitor visitor) {
        visitor.visitTerm(term);
        if (term instanceof GdlConstant) {
            visitor.visitConstant((GdlConstant) term);
        } else if (term instanceof GdlVariable) {
            visitor.visitVariable((GdlVariable) term);
        } else if (term instanceof GdlFunction) {
            visitFunction((GdlFunction) term, visitor);
        } else {
            throw new RuntimeException("Unexpected GdlTerm type " + term.getClass());
        }
    }
    private static void visitFunction(GdlFunction function, GdlVisitor visitor) {
        visitor.visitFunction(function);
        visitAll(function.getName(), visitor);
        visitAll(function.getBody(), visitor);
    }
}