struct Dog {
    name string
    age  int
}

struct Cat {
    name string
    age  int
}

interface Animal {
    say(s string)
    greet() int
}

fn (d Dog) say(s string) {
    println('Dog ${d.name}: "${s}"')
}

fn (c Cat) say(s string) {
    println('Cat ${c.name}: "${s}"')
}

fn (d Dog) greet() int {
    d.say('Hello!')
    return d.age
}

fn (c Cat) greet() int {
    c.say('Hello!')
    return c.age
}

fn use(a Animal) {
    if a is Dog {
        println('dog')
    } else if a is Cat {
        println('cat')
    } else {
        println('its a bug!')
    }
}

fn main() {
    use(Dog{'Doggo', 5})
    use(Cat{'Nyancat', 6})
}