debugging2.fs

open System
open System.Threading
open FSharp.Core.CompilerServices.StateMachineHelpers

type Cancellable<'T> =
    | Cancellable of (CancellationToken -> Result<'T, exn>)
    member inline cf.Invoke(ct: CancellationToken) =
        ct.ThrowIfCancellationRequested()
        let (Cancellable f) = cf
        f ct

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

     member inline _.Bind(computation1: Cancellable<'T>, [<InlineIfLambda>] continuation: 'T -> Cancellable<'TResult>) =
         Cancellable(fun ct -> 
             __debugPoint ""
             let v1 = computation1.Invoke(ct)
             match v1 with
             | Ok res1 -> 
                 let computation2 = continuation res1
                 computation2.Invoke(ct)
             | Error exn ->
                 Error exn)

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

let cancellable = CancellableBuilder()


//-------------------------------------------------------

let f1() =
    cancellable {
        Console.WriteLine("how are you")
        return 6
    }

let f2(path: bool) =
    cancellable {
        Console.WriteLine("step1")
        let! v1 = f1()
        Console.WriteLine("step2, v1 = ", v1)
        return v1
    }

let computation = f2(true)
let result = computation.Invoke(CancellationToken.None)