Function par_match

code/chapter03/infix_to_postfix.rs:39–43

同时检测多种括号

(open: char, close: char)

// 同时检测多种括号
fn par_match(open: char, close: char) -> bool {
    let opens = "([{";
    let closers = ")]}";
    opens.find(open) == closers.find(close)
}

// 检测括号是否匹配
fn par_checker3(infix: &str) -> bool {