写一个产生式系统实验 有完整代码

生成式系统通常用于自然语言处理、模式匹配和人工智能领域，其中一种常见的例子是基于上下文自由文法（Context-Free Grammar, CFG）的推导过程。下面是一个简单的Python实验，使用了`pyparsing`库来创建一个生成式系统。这个实验将实现一个基础的文法解析器。

from pyparsing import Word, alphas, nums, ParseException

# 定义基本的生成式规则
grammar = """
S -> NP VP
NP -> Det N | Det Adj N
VP -> Verb NP | Verb NP PP
PP -> P NP
Det -> "the" | "a"
Adj -> "red" | "big"
Verb -> "is" | "likes"
N -> "cat" | "dog" | "ball"
P -> "on"
"""

def parse_sentence(sentence):
    try:
        parser = grammar.parseString(sentence)
        print(f"Parsed sentence: {sentence}")
        print("Parse tree:")
        for item in parser[0]:
            print(item)
    except ParseException as e:
        print(f"Error parsing: {e.line}, message: {e.msg}")

# 测试
parse_sentence("The red dog is on the ball.")
parse_sentence("A big cat likes to play with a ball.")