struct KarmicVar<'a, T, U> {
    app: fn(&'a mut T) -> U
}
type Karma<T> = KarmicVar<'static, unit, T>

impl KarmicVar<'a, T, U> {
    fn pure(value: U) -> Self {
        KarmicVar {app: |_: &'a mut T| value}
    }
    fn bind<V>(&self, action: fn (U) -> KarmicVar<'a, T, V>) -> KarmicVar<'a, T, V> {
        KarmicVar {app: |karmic_ref: &'a mut T| action(self.app(karmic_ref))}
    }
}