给我一个LR(1)分析程序进行语法分析, 判断给出的符号串是否为该文法识别的句子的代码
时间: 2024-05-05 15:20:04 浏览: 13
下面是一个简单的LR(1)语法分析器代码示例,用于识别一个文法是否可以生成给定的符号串:
```python
# 定义文法
grammar = {
"S": [("A", "B"), ("C", "d")],
"A": [("a",)],
"B": [("b",)],
"C": [("A", "c"), ("d",)]
}
# 定义LR(1)自动机的状态
states = [
{
"S'": [("S",)],
"S": [("A", "B"), ("C", "d")],
"A": [("a",)],
"B": [("b",)],
"C": [("A", "c"), ("d",)]
},
{
"S'": [("S",)],
"S": [("A", "B"), ("C", "d")],
"C": [("A", "c"), ("d",)],
"A": [("a",)]
},
{
"S'": [("S",)],
"S": [("C", "d")],
"C": [("A", "c"), ("d",)],
"A": [("a",)]
},
{
"S'": [("S",)],
"S": [("C", "d")],
"C": [("d",)]
}
]
# 定义LR(1)自动机的动作表
actions = [
{"a": "s1", "c": "s2", "d": None},
{"b": "s3", "d": "r1", "$": "acc"},
{"c": "s2", "d": None, "$": "r3"},
{"d": None, "$": "r2"}
]
# 定义LR(1)自动机的Goto表
gotos = [
{"A": 1, "C": 2},
{},
{"A": 4},
{}
]
# 定义LR(1)语法分析器
def lr_parse(string):
stack = [0]
symbols = ["$"]
i = 0
while True:
state = states[stack[-1]]
if string[i] in actions[stack[-1]]:
action = actions[stack[-1]][string[i]]
elif "$" in actions[stack[-1]]:
action = actions[stack[-1]]["$"]
else:
return False
if action is None:
return False
elif action == "acc":
return True
elif action[0] == "s":
stack.append(int(action[1:]))
symbols.append(string[i])
i += 1
elif action[0] == "r":
production = list(grammar.items())[int(action[1:]) - 1]
lhs = production[0]
rhs = production[1]
for _ in rhs:
stack.pop()
symbols.pop()
symbols.append(lhs)
if symbols[-1] in gotos[stack[-1]]:
stack.append(gotos[stack[-1]][symbols[-1]])
else:
return False
else:
return False
```
该示例代码使用Python语言实现了一个简单的LR(1)语法分析器,用于识别一个给定的符号串是否可以由给定的文法生成。在这个例子中,我们定义了一个简单的文法和一个LR(1)自动机,该自动机有四个状态和两个表(动作表和Goto表)。我们还定义了一个函数`lr_parse`,该函数接受一个符号串,并使用上述LR(1)自动机来分析该符号串是否可以由给定的文法生成。如果该符号串可以被识别,则该函数返回True,否则返回False。
请注意,此示例代码是为了演示目的而编写的,可能不适用于更复杂的文法。对于更复杂的文法,可能需要使用更强大的语法分析器来进行处理。