PLY Lex and Yacc Issues

Question

我在使用PLY时遇到问题。我一直在阅读文档，并决定尝试这些例子。词法分析的例子运行得很好，但我无法进行解析。我也不明白如何将lex和yacc接口在一起以创建一个合适的编译器。解析器只包含lexer可能的标记，而且据我所知，没有其他内容。

我添加了一些东西，比如颜色（Colorama模块）和稍微不同的消息，但除此之外，这与示例相同：

#!/usr/bin/env python
### LEXICAL ANALYSIS ###

import ply.lex as lex
import colorama
colorama.init()
tokens = (
    "NUMBER",
    "PLUS",
    "MINUS",
    "MULTIPLY",
    "DIVIDE",
    "LBRACKET",
    "RBRACKET"
)

t_PLUS = r"+"
t_MINUS = r"-"
t_MULTIPLY = r"*"
t_DIVIDE = r"/"
t_LBRACKET = r"("
t_RBRACKET = r")"
t_ignore = "tr "
def t_NUMBER(t):
    r"d+"
    t.value = int(t.value)
    return t
def t_newline(t):
    r"n+"
    t.lexer.lineno += len(t.value)
def t_COMMENT(t):
    r"#.*"
    print "Comment:", t.value
def t_error(t):
    print colorama.Fore.RED + "nnLEXICAL ERROR: line", t.lexer.lineno, "and position", t.lexer.lexpos, "invalid token:", t.value.split("n")[0] + colorama.Fore.RESET
    t.lexer.skip(len(t.value))

def mylex(inp):
    lexer = lex.lex()
    lexer.input(inp)

    for token in lexer:
        print "Token:", token

这很好，但解析器却不行：

#!/usr/bin/env python

import ply.yacc as yacc
from langlex import tokens
def p_expression_plus(p):
    "expression : expression PLUS term"
    p[0] = p[1] + p[3]
def p_expression_minus(p):
    "expression : expression MINUS term"
    p[0] = p[1] - p[3]
def p_expression_term(p):
    "expression : term"
    p[0] = p[1]
def p_term_times(p):
    "term : term MULTIPLY factor"
    p[0] = p[1] * p[3]
def p_term_div(p):
    "term : term DIVIDE factor"
    p[0] = p[1] / p[3]
def p_term_factor(p):
    "term : factor"
    p[0] = p[1]
def p_factor_num(p):
    "factor : NUMBER"
    p[0] = p[1]
def p_factor_expr(p):
    "factor : LBRACKET expression RBRACKET"
    p[0] = p[2]
def p_error(p):
    print "Syntax error!"
parser = yacc.yacc()
while True:
    s = raw_input("calc > ")
    if not(s):
        continue
    result = parser.parse(s)
    print result

当我尝试运行它时，我得到以下错误：

calc > 5 + 10
Traceback (most recent call last):
  File "C:UsersMaxDesktoplanglangyacc.py", line 49, in <module>
    result = parser.parse(s)
  File "C:Python27libsite-packagesplyyacc.py", line 265, in parse
    return self.parseopt_notrack(input,lexer,debug,tracking,tokenfunc)
  File "C:Python27libsite-packagesplyyacc.py", line 881, in parseopt_notrack
    lexer = lex.lexer
AttributeError: 'module' object has no attribute 'lexer'

我是lex、yacc和编译器开发的初学者，不知道为什么会发生这种情况。如有任何帮助，我们将不胜感激。

Answer 1

您尚未在lexer文件中构建lexer。您在函数mylex()中有它，但实际上并没有构建它。

将其从功能中拉出。

lexer = lex.lex()
def mylex(inp):
    lexer.input(inp)
    # etc.