{{{
#!rst
public class GnappoProduct {
    /**
     * @param args
     * @throws SchemeException
     */
    public static void main(String[] args) throws SchemeException {
        // TODO Auto-generated method stub
        SchemeFactoryManager fm = SchemeFactoryManager.instance();

        fm.put("pow",
            new SchemeFactory() {
                public SchemeExpression create(Object... args) {
                    return new SchemeExpressionPower((SchemeExpression) args[0],
                        (SchemeExpression) args[1]);
                }
            });

        SchemeExpression power = fm.create("pow",
                fm.create("SchemeExpressionInt", 2),
                fm.create("SchemeExpressionInt", 4));

        power.prettyPrint(System.out);
        System.out.println();
        System.out.print(power.evaluate(null));
    }

    private static class SchemeExpressionPower extends SchemeExpressionAbstract {
        private SchemeExpression exp1;
        private SchemeExpression exp2;

        public SchemeExpressionPower(SchemeExpression expr1,
            SchemeExpression expr2) {
            exp1 = expr1;
            exp2 = expr2;
        }

        public SchemeValue evaluate(SchemeEnvironment env)
            throws SchemeException {
            return SchemeFactoryManager.instance()
                                       .create("SchemeExpressionInt",
                ((int) (Math.pow(exp1.evaluate(env).asInt(),
                    exp2.evaluate(env).asInt())))).evaluate(env);
        }

        public void prettyPrint(PrintStream out) {
            out.print("(pow ");
            exp1.prettyPrint(out);
            out.print(" ");
            exp2.prettyPrint(out);
            out.print(")");
        }
    }
}
}}}