rust - 使用Nom将整数解析为浮点型

Nom有一个example of parsing a floating point number:

named!(unsigned_float <f32>, map_res!(
  map_res!(
    recognize!(
      alt!(
        delimited!(digit, tag!("."), opt!(complete!(digit))) |
        delimited!(opt!(digit), tag!("."), digit)
      )
    ),
    str::from_utf8
  ),
  FromStr::from_str
));

我想扩展此示例，使其也支持将"123"解析为123.0。我已经尝试过这种运气不好的事情:

named!(unsigned_float_v1 <f32>,
    map_res!(
        map_res!(
            alt!(
                recognize!(
                    alt!(
                        delimited!(digit, tag!("."), opt!(complete!(digit))) |
                        delimited!(opt!(digit), tag!("."), digit)
                    )
                ) |
                ws!(digit)
            ),
            str::from_utf8
        ),
        FromStr::from_str
    )
);

named!(unsigned_float_v2 <f32>,
    map_res!(
        map_res!(
            recognize!(
                alt!(
                    delimited!(digit, tag!("."), opt!(complete!(digit))) |
                    delimited!(opt!(digit), tag!("."), digit) |
                    digit
                )
            ),
            str::from_utf8
        ),
        FromStr::from_str
    )
);

最佳答案

您还需要用tag!(".")包装complete!，如下所示:

named!(unsigned_float_v2 <f32>,
    map_res!(
        map_res!(
            recognize!(
                alt!(
                    delimited!(digit, complete!(tag!(".")), opt!(complete!(digit))) |
                    delimited!(opt!(digit), complete!(tag!("."), digit) |
                    digit
                )
            ),
            str::from_utf8
        ),
        FromStr::from_str
    )
);

如果输入是123，则tag!将返回Incomplete，因为它无法确定下一个输入是否是.

关于rust - 使用Nom将整数解析为浮点型，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/42790494/