public static Statement Loop(Expression cond, StatementBlock block)
 {
     throw new NotImplementedException ();
 }
        public static Statement For(List<Statement> init,
			Expression cond,
			Statement cont,
			StatementBlock body)
        {
            return new ForStatement (init, cond, cont, body);
        }
 public static Statement IfThen(Expression cond, StatementBlock trueBlock)
 {
     return new IfStatement (cond, trueBlock, null);
 }
        public ForStatement(List<Statement> init,
			Expression cond,
			Statement cont,
			StatementBlock body)
        {
            Initializers = init;
            Condition = cond;
            Continuer = cont;
            Body = body;
        }