如何使用nom将带符号的字符串解析为i32？

[dependencies]
nom = "6.2.1"

use nom::character::complete::{char, digit1};
use nom::combinator::map_res;
use nom::sequence::tuple;
use nom::IResult;

fn parse_signed_int(input: &str) -> IResult<&str, i32> {
    let (input, sign) = char('-')(input)?;
    let (input, digits) = digit1(input)?;
    let parsed_int: Result<i32, _> = digits.parse();
    match parsed_int {
        Ok(value) => {
            if sign == '-' {
                Ok((input, -value))
            } else {
                Ok((input, value))
            }
        }
        Err(_) => Err(nom::Err::Failure((input, nom::error::ErrorKind::Digit))),
    }
}

fn main() {
    let input = "-123";
    match parse_signed_int(input) {
        Ok((_, value)) => println!("Parsed value: {}", value),
        Err(e) => println!("Parsing error: {:?}", e),
    }
}