在ply-递归中允许语法构造?

这可能是以前问过,但我不知道要搜索什么,真的。假设我有一些字符串,我想用它构建一个解析器。

我有弦 a OR b , b OR C 而且 a OR (b AND c) . 现在嵌套的括号给我带来了麻烦,我不知道如何构造适当的 p_* 功能。允许递归吗?如果是这样,怎么办?

import ply.lex as lex
import ply.yacc as yacc

# List of token names.   This is always required
tokens = (
    'VARIABLE',
    'OR',
    'AND',
    'PAR_OPEN',
    'PAR_CLOSE',
)

# Regular expression rules for simple tokens
t_ignore        = ' \t'
t_VARIABLE      = r'\b[a-z]+\b'
t_OR            = r'\bOR\b'
t_AND           = r'\bAND\b'
t_PAR_OPEN      = r'\('
t_PAR_CLOSE     = r'\)'

def t_error(t):
    print("Illegal character '%s'" % t.value[0])
    t.lexer.skip(1)

# Build the lexer
lexer = lex.lex()

def p_term(p):
    '''term : VARIABLE OR VARIABLE
            | VARIABLE AND VARIABLE
            | PAR_OPEN VARIABLE AND VARIABLE PAR_CLOSE'''

    if p[2] == 'AND':
        p[0] = "".join([p[1], p[3]])

    for idx, val in enumerate(p):
        print(idx, val)

def p_error(p):
    print("Syntax error in input!")
    print(p)


parser = yacc.yacc()
res = parser.parse("(a AND b)")
print(res)

我还想用例如 res = parser.parse("a OR (b AND c)") 但无济于事。