# File kwartz.rb, line 2327
        def translate_expr(node, code='', level=0)
            case tkn = node.token
            when :variable
                code << '$'
                super(node, code, level)
            when :empty, :notempty
                ## s==empty => '!s', s!=empty => 's'
                left = node.left
                node2 = tkn == :empty ? ExprNode.new('!', left, nil) : left
                translate_expr(node2, code, level)
            else
                super(node, code, level)
            end
            return code
        end