参考资料中未直接提供实验三算符优先分析的源程序。不过可以根据实验要求和算法思想来构建源程序。以下是一个简单的Python示例，用于实现算符优先分析的部分功能，包括计算FIRSTVT集、LASTVT集和构造算符优先关系表： ```python # 定义文法类 class Grammar: def __init__(self, productions): self.productions = productions self.non_terminals = set() self.terminals = set() self.firstvt = {} self.lastvt = {} self.priority_table = {} # 提取非终结符和终结符 for left, right in productions: self.non_terminals.add(left) for symbol in right: if symbol.isupper(): self.non_terminals.add(symbol) else: self.terminals.add(symbol) # 计算FIRSTVT集 def compute_firstvt(self): for non_terminal in self.non_terminals: self.firstvt[non_terminal] = set() changed = True while changed: changed = False for left, right in self.productions: first_symbol = right[0] if first_symbol in self.terminals: if first_symbol not in self.firstvt[left]: self.firstvt[left].add(first_symbol) changed = True elif first_symbol in self.non_terminals: for terminal in self.firstvt[first_symbol]: if terminal not in self.firstvt[left]: self.firstvt[left].add(terminal) changed = True # 计算LASTVT集 def compute_lastvt(self): for non_terminal in self.non_terminals: self.lastvt[non_terminal] = set() changed = True while changed: changed = False for left, right in self.productions: last_symbol = right[-1] if last_symbol in self.terminals: if last_symbol not in self.lastvt[left]: self.lastvt[left].add(last_symbol) changed = True elif last_symbol in self.non_terminals: for terminal in self.lastvt[last_symbol]: if terminal not in self.lastvt[left]: self.lastvt[left].add(terminal) changed = True # 构造算符优先关系表 def construct_priority_table(self): self.priority_table = {t1: {t2: None for t2 in self.terminals} for t1 in self.terminals} for left, right in self.productions: for i in range(len(right) - 1): current = right[i] next_symbol = right[i + 1] if current in self.terminals and next_symbol in self.terminals: self.priority_table[current][next_symbol] = '=' if current in self.terminals and next_symbol in self.non_terminals: for terminal in self.firstvt[next_symbol]: self.priority_table[current][terminal] = '<' if current in self.non_terminals and next_symbol in self.terminals: for terminal in self.lastvt[current]: self.priority_table[terminal][next_symbol] = '>' # 示例文法 productions = [ ('S', '#E#'), ('P', 'i'), ('F', 'P'), ('T', 'F'), ('E', 'T'), ('E', 'E+T') ] # 创建文法对象 grammar = Grammar(productions) # 计算FIRSTVT集 grammar.compute_firstvt() print("FIRSTVT集:", grammar.firstvt) # 计算LASTVT集 grammar.compute_lastvt() print("LASTVT集:", grammar.lastvt) # 构造算符优先关系表 grammar.construct_priority_table() print("算符优先关系表:") for t1 in grammar.terminals: for t2 in grammar.terminals: print(f"{t1} {t2}: {grammar.priority_table[t1][t2]}") ``` ###