what.rs

struct TokenizationStep(fn(
    runes: dyn Iterator<Item=io::Result<String>>,
    stack: dyn Iterator<Item=TokenizationStep>) -> io::Result<Box<dyn Iterator<Item=Box<dyn Token>>>>);

fn parseFile(runes: impl Iterator<Item=io::Result<String>>, stack: Box<dyn Iterator<Item=TokenizationStep>>) -> io::Result<Box<impl Iterator<Item=Box<impl Token>>>> {
    return parseText(runes, stack)
}

struct Text(String);

fn parseText(runes: impl Iterator<Item=io::Result<String>>, stack: Box<dyn Iterator<Item=TokenizationStep>>) -> io::Result<Box<impl Iterator<Item=Box<impl Token>>>> {
    let mut text: Vec<String> = Vec::new();
    for rune in runes {
        match rune {
            Ok(v) => match v {
                '[' => match text.len() {
                    0 => text.return parseTag([v].iter().chain(runes), [parseFile].iter().chain(stack)),
                    _ => [Text(text)].chain(text.return parseTag([v].iter().chain(runes), [parseFile].iter().chain(stack))
                _ => text.push(v)
            },
            Err(e) => e
        }
    }
}