问：

TL;博士：

如何对语法的产生进行计算建模，使同一左手边存在无限数量的乘积？

我正在做一个关于形式语言理论的项目，并试图编写一个用于构建常规语法对象的类，这些对象可以传递给有限状态机。我幼稚的尝试是创建一个 API，用于为每个允许的输入添加一个产品。我的尝试的精简版本如下（基于形式语法的形式定义）：G = (N, Σ, P, S)

class ContextFreeGrammar:
    def __init__(self, variables, alphabet, production_rules, start_variable):
        self.variables = variables
        self.alphabet = alphabet
        self.production_rules = production_rules
        self.start_variable = start_variable

    def __repr__(self):
        return '{}({}, {}, {}, {})'.format(
            self.__class__.__name__,
            self.variables,
            self.alphabet,
            self.production_rules,
            self.start_variable
        )


class RegularGrammar(ContextFreeGrammar):
    _regular_expression_grammar = None # TODO

    @classmethod
    def from_regular_expression(cls, regular_expression):
        raise NotImplementedError()

我还没有真正写有限状态自动机或下推自动机。

正则表达式的语法与上下文无关，因此我在下面的 WSN 中包含了我的定义：

syntax = expression .
expression = term "|" expression .
expression = term .
term = factor repetition term .
term = factor term .
term = .
repetition = "*" .
repetition = "+" .
repetition = "?" .
repetition = "{" nonnegative_integer "," nonnegative_integer "}" .
repetition = "{" nonnegative_integer ",}" .
repetition = "{," nonnegative_integer "}" .
nonnegative_integer = nonzero_arabic_numeral arabic_numerals .
nonnegative_integer = arabic_numeral .
nonzero_arabic_numeral = "1" .
nonzero_arabic_numeral = "2" .
nonzero_arabic_numeral = "3" .
nonzero_arabic_numeral = "4" .
nonzero_arabic_numeral = "5" .
nonzero_arabic_numeral = "6" .
nonzero_arabic_numeral = "7" .
nonzero_arabic_numeral = "8" .
nonzero_arabic_numeral = "9" .
arabic_numeral = nonzero_arabic_numeral .
arabic_numeral = "0" .
arabic_numerals = arabic_numeral .
arabic_numerals = arabic_numeral arabic_numerals .
factor = "(" expression ")" .
factor = character_class .
factor = character .
escaped_character = "\\." .
escaped_character = "\\(" .
escaped_character = "\\)" .
escaped_character = "\\+" .
escaped_character = "\\*" .
escaped_character = "\\?" .
escaped_character = "\\[" .
escaped_character = "\\]" .
escaped_character = "\\\\" .
escaped_character = "\\{" .
escaped_character = "\\}" .
escaped_character = "\\|" .
character -> TODO ;
character_class = TODO .

人们可以很容易地看出，我明确地将交替分成单独的作品。我这样做是为了便于实施。但是我被困在我应该如何去做角色课程之类的事情上。我想成为一张地图，从每个左手边到一组对应的右手边。但现在看来，这不可行。production_rules