LR0分析程序的设计与实现代码

以下是一个简单的 LR(0) 分析程序的设计与实现代码，用 Python 语言实现：

# LR(0) 分析程序

# 标识符常量
SHIFT = 1
REDUCE = 2
ACCEPT = 3
ERROR = 4

# 产生式类
class Production:
    def __init__(self, head, body):
        self.head = head
        self.body = body

# 项目类
class Item:
    def __init__(self, production, dot):
        self.production = production
        self.dot = dot

    def __eq__(self, other):
        return self.production == other.production and self.dot == other.dot

    def __hash__(self):
        return hash(str(self.production) + str(self.dot))

# LR(0) 分析表类
class LR0Table:
    def __init__(self, grammar):
        self.grammar = grammar
        self.actions = {}
        self.gotos = {}

        # 构造项目集规范族
        self.canonical_collection = self.build_canonical_collection()

        # 构造 LR(0) 分析表
        self.build_table()

    # 构造项目集规范族
    def build_canonical_collection(self):
        # 第一步：初始化
        start_production = self.grammar.productions[0]
        start_item = Item(start_production, 0)
        closure = self.closure(set([start_item]))
        current_state = frozenset(closure)
        canonical_collection = {current_state: closure}

        # 第二步：循环直到项目集规范族没有变化
        while True:
            for item in current_state:
                # 对于每个项目 A -> α·Bβ，进行 GOTO 操作
                if not item.dot == len(item.production.body):
                    symbol = item.production.body[item.dot]
                    goto = self.goto(current_state, symbol)
                    if not goto in canonical_collection:
                        closure = self.closure(goto)
                        canonical_collection[goto] = closure

            # 如果项目集规范族没有变化，则退出循环
            if len(canonical_collection) == len(current_state):
                break
            else:
                current_state = list(canonical_collection.keys())[-1]

        return canonical_collection

    # 求闭包
    def closure(self, items):
        closure = set(items)
        while True:
            new_items = set()
            for item in closure:
                # 对于每个项目 A -> α·Bβ，将 B -> γ 加入 new_items
                if not item.dot == len(item.production.body):
                    symbol = item.production.body[item.dot]
                    if symbol in self.grammar.non_terminals:
                        for production in self.grammar.productions:
                            if production.head == symbol:
                                new_item = Item(production, 0)
                                if not new_item in closure:
                                    new_items.add(new_item)
            if not new_items:
                break
            closure |= new_items

        return closure

    # 求 GOTO(A -> α·Bβ, b)
    def goto(self, items, symbol):
        goto = set()
        for item in items:
            if not item.dot == len(item.production.body) and item.production.body[item.dot] == symbol:
                goto.add(Item(item.production, item.dot + 1))
        return frozenset(self.closure(goto))

    # 构造 LR(0) 分析表
    def build_table(self):
        for i, state in enumerate(self.canonical_collection):
            # 对于每个项目 A -> α·，将 ACTION[s, a] 设为 SHIFT(t)，其中 t = GOTO[s, a]
            for item in state:
                if item.dot == len(item.production.body):
                    if item.production.head == self.grammar.start_symbol:
                        self.actions[(i, '$')] = (ACCEPT, None)
                    else:
                        for symbol in self.grammar.follow(item.production.head):
                            self.actions[(i, symbol)] = (REDUCE, item.production)
                else:
                    symbol = item.production.body[item.dot]
                    goto = self.goto(state, symbol)
                    if symbol in self.grammar.terminals:
                        self.actions[(i, symbol)] = (SHIFT, goto)
                    else:
                        self.gotos[(i, symbol)] = goto

    # 执行 LR(0) 分析
    def parse(self, input):
        stack = [0]
        output = []
        while True:
            state = stack[-1]
            symbol = input[0]
            if (state, symbol) in self.actions:
                action, arg = self.actions[(state, symbol)]
                if action == SHIFT:
                    stack.append(arg)
                    input = input[1:]
                elif action == REDUCE:
                    head = arg.head
                    body = arg.body
                    output.append(arg)
                    for i in range(len(body)):
                        stack.pop()
                    state = stack[-1]
                    stack.append(self.gotos[(state, head)])
                elif action == ACCEPT:
                    output.append(arg)
                    return output
                else:
                    raise Exception('Syntax error')
            else:
                raise Exception('Syntax error')

此代码实现了 LR(0) 分析程序的主要功能，包括构造项目集规范族、构造 LR(0) 分析表和执行 LR(0) 分析。使用时需要提供一个文法对象（包括产生式和起始符号）和一个输入串。输出为分析树或语法错误。