debugging1.fs

open System
open System.Threading

type Cancellable<'T> = delegate of CancellationToken -> 'T

type CancellableBuilder() =
     member _.Delay(body: unit -> Cancellable<'T>) =
         Cancellable(fun ct -> 
             let computation = body()
             computation.Invoke(ct))

     member _.Bind(computation1: Cancellable<'T>, continuation: 'T -> Cancellable<'TResult>) =
         Cancellable(fun ct -> 
             let v1 = computation1.Invoke(ct)
             let computation2 = continuation v1
             computation2.Invoke(ct))

     member _.Return(v: 'T) =
         Cancellable(fun ct -> v)

let cancellable = CancellableBuilder()

let f1() =
    cancellable {
        System.Console.WriteLine("hello")
        return 4
    }

let f2() =
    cancellable {
        System.Console.WriteLine("world")
        return 5
    }

let f3() =
    cancellable {
        let! v1 = f1()
        let! v2 = f2()
        return v1 + v2
    }

let computation = f3()
let result = computation.Invoke(CancellationToken.None)