Method parse

examples/final.rs:31–42

(command: &'a str)

impl<'a> Chain<'a> {
    fn parse(command: &'a str) -> Option<Self> {
        let mut tokens = command.split_whitespace().peekable();
        let mut elements = vec![];
        while let Some(e) = Element::parse_next(&mut tokens) {
            elements.push(e);
        }
        if !elements.is_empty() {
            Some(Self { elements })
        } else {
            None
        }
    }

    fn run(self) {
        let mut prev_output: Option<Output> = None;