package org.apidesign.visitor;

public final class Language {

    private Language() { }

    public interface Expression {

        public abstract void visit(Visitor v);

    }

    public interface Plus extends Expression {

        public Expression getFirst();

        public Expression getSecond();

    }

    public interface Number extends Expression {

        public int getValue();

    }

    // BEGIN: visitor.clientprovider.v2

    /** @since 2.0 */

    public interface Minus extends Expression {

        public Expression getFirst();

        public Expression getSecond();

    }

    public static abstract class Visitor {

        Visitor() {}

        /** @since 2.0 */

        public static Visitor create(Version20 v) {

            return create20(v);

        }

        /** @since 2.0 */

        public interface Version20 extends Version10 {

            public void visitMinus(Minus m);

        }

        /** @since 2.0 */

        public abstract void dispatchNumber(Number n);

    // FINISH: visitor.clientprovider.v2

        public static Visitor create(Version10 v) {

            return create10(v);

        }

        public interface Version10 {

            public boolean visitUnknown(Expression e);

            public void visitPlus(Plus s);

            public void visitNumber(Number n);

        }

        public abstract void dispatchPlus(Plus p);

        public abstract void dispatchMinus(Minus m);

    }

    static Visitor create10(final Visitor.Version10 v) {

        return new Visitor() {

            @Override

            public void dispatchPlus(Plus p) {

                v.visitPlus(p);

            }

            @Override

            public void dispatchNumber(Number n) {

                v.visitNumber(n);

            }

            @Override

            public void dispatchMinus(Minus m) {

                if (v.visitUnknown(m)) {

                    m.getFirst().visit(this);

                    m.getSecond().visit(this);

                }

            }

        };

    }

    static Visitor create20(final Visitor.Version20 v) {

        return new Visitor() {

            @Override

            public void dispatchPlus(Plus p) {

                v.visitPlus(p);

            }

            @Override

            public void dispatchNumber(Number n) {

                v.visitNumber(n);

            }

            @Override

            public void dispatchMinus(Minus m) {

                v.visitMinus(m);

            }

        };

    }

}