gistfile1.rs

// `parts` is an Iterator<Item=&str>
// `conv_mod` returns a `Result<Vec<String>, _>`

        let themod = if parts.peek().is_some() {
            if !parts.peek().unwrap().starts_with("Key") {
                Some(conv_mod(parts.next().unwrap())?)
            } else {
                None
            }
        } else {
            None
        };

v2.rs

// thanks smitra

        let themod = parts.peek().map(|p| {
            if !p.starts_with("Key") {
                Some(conv_mod(parts.next().unwrap())?)
            } else {
                None
            }
        });