Code shared from the Rust Playground

playground.rs

fn nom_str_until_eol(i: &str) -> nom::IResult<&str, &str> {
    let first_line = i.lines().next();
    if let Some(first_line) = first_line {
        let rest = &i[first_line.len()..];
        let rest = rest.trim();
        Ok((rest, first_line))
    } else {
        Ok((i, ""))
    }
}

fn nom_comment(i: &str) -> nom::IResult<&str, &str> {
    let(i, _) = tag("%")(i)?;
    let(i, comment) = nom_str_until_eol(i)?;
    Ok((i, comment))
}

fn nom_other_thing(i: &str) -> nom::IResult<&str, &str> {
    let(i, _) = tag("fn")(i)?;
    let(i, function_line) = nom_str_until_eol(i)?;
    Ok((i, function_line))
}

fn nom_either(i: &str) -> nom::IResult<&str, &str> {
    alt(nom_comment, nom_other_thing)(i)
}