完整 Lexer 跑一遍的四个数

把完整的 Lexer 跑在那段源码上，输出四个数：词数、关键字数、字符串那个词的字符数、最后一个词的列号。

let rate = 12;
let msg = "hi there";
total = rate >= 3;

玩具语言的词法规则：关键字 let if else while；标识符以字母或下划线开头；数字是连续的数位；字符串用一对双引号括起来（不含转义）；双字符运算符 >= <= == !=；单字符运算符 + - * / = < > ; ( )；空白只做分隔。

KEYWORDS = ("let", "if", "else", "while")
TWO = ("==", "!=", ">=", "<=")
ONE = "+-*/=<>;()"
SRC = 'let rate = 12;\nlet msg = "hi there";\ntotal = rate >= 3;'

import re
PAT = re.compile(r'(?:let|if|else|while)\b|[A-Za-z_]\w*|\d+|"[^"]*"'
                 r'|==|!=|>=|<=|[+\-*/=<>;()]')
toks = [m.group() for m in PAT.finditer(SRC)]
kw = sum(1 for t in toks if t in KEYWORDS)
st = next(t for t in toks if t.startswith('"'))
last_line = SRC.split("\n")[-1]
col = last_line.rfind(";") + 1
print("/".join(str(x) for x in (len(toks), kw, len(st), col)))