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Call/CC for Async

An implementation of call-with-current-continuation for Async.

Async.callcc

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let callcc (f: ('a -> Async<'b>) -> Async<'a>) : Async<'a> =
  Async.FromContinuations(fun (cont, econt, ccont) ->
    Async.StartWithContinuations(f (fun a -> Async.FromContinuations(fun (_, _, _) -> cont a)), cont, econt, ccont))

Test sample

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(* Test callcc *)
let sum l =
  let rec sum l = async {
    let! result = callcc (fun exit1 -> async {
      match l with
      | [] -> return 0
      | h::t when h = 2 -> return! exit1 42
      | h::t -> let! r = sum t
                return h + r })
    return result }
  Async.RunSynchronously(sum l)

[<Test>]
let ``When summing a list without a 2 via callcc it should return 8``() =
  sum [1;1;3;3] |> should equal 8

[<Test>]
let ``When summing a list containing 2 via callcc it should return 43``() =
  sum [1;2;3] |> should equal 43
val callcc : f:(('a -> Async<'b>) -> Async<'a>) -> Async<'a>

Full name: Script.callcc
val f : (('a -> Async<'b>) -> Async<'a>)
Multiple items
type Async
static member AsBeginEnd : computation:('Arg -> Async<'T>) -> ('Arg * AsyncCallback * obj -> IAsyncResult) * (IAsyncResult -> 'T) * (IAsyncResult -> unit)
static member AwaitEvent : event:IEvent<'Del,'T> * ?cancelAction:(unit -> unit) -> Async<'T> (requires delegate and 'Del :> Delegate)
static member AwaitIAsyncResult : iar:IAsyncResult * ?millisecondsTimeout:int -> Async<bool>
static member AwaitTask : task:Task<'T> -> Async<'T>
static member AwaitWaitHandle : waitHandle:WaitHandle * ?millisecondsTimeout:int -> Async<bool>
static member CancelDefaultToken : unit -> unit
static member Catch : computation:Async<'T> -> Async<Choice<'T,exn>>
static member FromBeginEnd : beginAction:(AsyncCallback * obj -> IAsyncResult) * endAction:(IAsyncResult -> 'T) * ?cancelAction:(unit -> unit) -> Async<'T>
static member FromBeginEnd : arg:'Arg1 * beginAction:('Arg1 * AsyncCallback * obj -> IAsyncResult) * endAction:(IAsyncResult -> 'T) * ?cancelAction:(unit -> unit) -> Async<'T>
static member FromBeginEnd : arg1:'Arg1 * arg2:'Arg2 * beginAction:('Arg1 * 'Arg2 * AsyncCallback * obj -> IAsyncResult) * endAction:(IAsyncResult -> 'T) * ?cancelAction:(unit -> unit) -> Async<'T>
static member FromBeginEnd : arg1:'Arg1 * arg2:'Arg2 * arg3:'Arg3 * beginAction:('Arg1 * 'Arg2 * 'Arg3 * AsyncCallback * obj -> IAsyncResult) * endAction:(IAsyncResult -> 'T) * ?cancelAction:(unit -> unit) -> Async<'T>
static member FromContinuations : callback:(('T -> unit) * (exn -> unit) * (OperationCanceledException -> unit) -> unit) -> Async<'T>
static member Ignore : computation:Async<'T> -> Async<unit>
static member OnCancel : interruption:(unit -> unit) -> Async<IDisposable>
static member Parallel : computations:seq<Async<'T>> -> Async<'T []>
static member RunSynchronously : computation:Async<'T> * ?timeout:int * ?cancellationToken:CancellationToken -> 'T
static member Sleep : millisecondsDueTime:int -> Async<unit>
static member Start : computation:Async<unit> * ?cancellationToken:CancellationToken -> unit
static member StartAsTask : computation:Async<'T> * ?taskCreationOptions:TaskCreationOptions * ?cancellationToken:CancellationToken -> Task<'T>
static member StartChild : computation:Async<'T> * ?millisecondsTimeout:int -> Async<Async<'T>>
static member StartChildAsTask : computation:Async<'T> * ?taskCreationOptions:TaskCreationOptions -> Async<Task<'T>>
static member StartImmediate : computation:Async<unit> * ?cancellationToken:CancellationToken -> unit
static member StartWithContinuations : computation:Async<'T> * continuation:('T -> unit) * exceptionContinuation:(exn -> unit) * cancellationContinuation:(OperationCanceledException -> unit) * ?cancellationToken:CancellationToken -> unit
static member SwitchToContext : syncContext:SynchronizationContext -> Async<unit>
static member SwitchToNewThread : unit -> Async<unit>
static member SwitchToThreadPool : unit -> Async<unit>
static member TryCancelled : computation:Async<'T> * compensation:(OperationCanceledException -> unit) -> Async<'T>
static member CancellationToken : Async<CancellationToken>
static member DefaultCancellationToken : CancellationToken

Full name: Microsoft.FSharp.Control.Async

--------------------
type Async<'T>

Full name: Microsoft.FSharp.Control.Async<_>
static member Async.FromContinuations : callback:(('T -> unit) * (exn -> unit) * (System.OperationCanceledException -> unit) -> unit) -> Async<'T>
val cont : ('a -> unit)
val econt : (exn -> unit)
val ccont : (System.OperationCanceledException -> unit)
static member Async.StartWithContinuations : computation:Async<'T> * continuation:('T -> unit) * exceptionContinuation:(exn -> unit) * cancellationContinuation:(System.OperationCanceledException -> unit) * ?cancellationToken:System.Threading.CancellationToken -> unit
val a : 'a
val sum : l:int list -> int

Full name: Script.sum
val l : int list
val sum : (int list -> Async<int>)
val async : AsyncBuilder

Full name: Microsoft.FSharp.Core.ExtraTopLevelOperators.async
val result : int
val exit1 : (int -> Async<int>)
val h : int
val t : int list
val r : int
static member Async.RunSynchronously : computation:Async<'T> * ?timeout:int * ?cancellationToken:System.Threading.CancellationToken -> 'T
val ( When summing a list without a 2 via callcc it should return 8 ) : unit -> 'a

Full name: Script.( When summing a list without a 2 via callcc it should return 8 )
val ( When summing a list containing 2 via callcc it should return 43 ) : unit -> 'a

Full name: Script.( When summing a list containing 2 via callcc it should return 43 )

More information

Link:http://fssnip.net/7U
Posted:5 years ago
Author:Ryan Riley
Tags: async , continuation , callcc