rust - 解析允许在 nom 中嵌套括号

Question

我用的是名。我想解析一个被括号包围的字符串，并允许在字符串中添加额外的嵌套括号。

所以(a + b)会解析为a + b，并且((a + b))会解析为(a + b)

这适用于第一种情况，但不适用于嵌套情况：

pub fn parse_expr(input: &str) -> IResult<&str, &str> {
    // TODO: this will fail with nested parentheses, but `rest` doesn't seem to
    // be working.
    delimited(tag("("), take_until(")"), tag(")"))(input)
}

我尝试使用rest，但这不尊重 final )：

pub fn parse_expr(input: &str) -> IResult<&str, &str> {
    delimited(tag("("), rest, tag(")"))(input)
}

谢谢！

Answer 1

我在 nom 问题日志中找到了对此的引用：https ://github.com/Geal/nom/issues/1253

我正在使用这个函数，基本上是这个https://docs.rs/parse-hyperlinks/0.23.3/src/parse_hyperlinks/lib.rs.html#41parse_hyperlinks的手写解析器：

pub fn take_until_unbalanced(
    opening_bracket: char,
    closing_bracket: char,
) -> impl Fn(&str) -> IResult<&str, &str> {
    move |i: &str| {
        let mut index = 0;
        let mut bracket_counter = 0;
        while let Some(n) = &i[index..].find(&[opening_bracket, closing_bracket, '\\'][..]) {
            index += n;
            let mut it = i[index..].chars();
            match it.next().unwrap_or_default() {
                c if c == '\\' => {
                    // Skip the escape char `\`.
                    index += '\\'.len_utf8();
                    // Skip also the following char.
                    let c = it.next().unwrap_or_default();
                    index += c.len_utf8();
                }
                c if c == opening_bracket => {
                    bracket_counter += 1;
                    index += opening_bracket.len_utf8();
                }
                c if c == closing_bracket => {
                    // Closing bracket.
                    bracket_counter -= 1;
                    index += closing_bracket.len_utf8();
                }
                // Can not happen.
                _ => unreachable!(),
            };
            // We found the unmatched closing bracket.
            if bracket_counter == -1 {
                // We do not consume it.
                index -= closing_bracket.len_utf8();
                return Ok((&i[index..], &i[0..index]));
            };
        }

        if bracket_counter == 0 {
            Ok(("", i))
        } else {
            Err(Err::Error(Error::from_error_kind(i, ErrorKind::TakeUntil)))
        }
    }
}