//more abstract pattern of counter using scheduler.
//this requires that compiler can define a recursive closure inside function using `letrec`.
fn makecounter(){
    let x = 0.0
    letrec gen = | |{
        x = x+1.0
       | |{gen()}@(now+1.0)
    }
    | |{gen() }@1.0
    let getter = | | {x}
    getter
}
let x_getter = makecounter();
fn dsp(){
    x_getter()
}