#[derive(Debug)]
enum View<T> {
    Label { text: String },
    Button { text: String, on_click: T },
    VerticalLayout(Vec<View<T>>),
}
use View::*;

fn render<T: std::fmt::Debug>(v: View<T>) -> String {
    let s = match v {
        Label { text } =>
            text,
        Button { text, .. } =>
            format!("[{}]", text),
        VerticalLayout(l) =>
            l.into_iter().map(render).collect::<Vec<String>>().join("\n")
    };
    return s;
}



type Model = i32;

#[derive(Debug)]
enum Msg {
    Increment,
    Decrement,
}
use Msg::*;

fn view(model: Model) -> View<Msg> {
    return VerticalLayout(vec![
        Button { text: "-".to_string(), on_click: Increment },
        Label { text: model.to_string(), },
        Button { text: "+".to_string(), on_click: Decrement },
    ]);
}

fn update(model: Model, msg: Msg) -> Model {
    return match msg {
        Increment =>
            model + 1,
        Decrement =>
            model - 1
    }
}

fn main() {
    let m1 = 0;
    let m2 = update(m1, Decrement);
    println!("{}", render(view(m2)));
}