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Async.Choice

A simple extension method for asynchronous non-deterministic computations.

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open System

[<AutoOpen>]
module AsyncEx = 
    type private SuccessException<'T>(value : 'T) =
        inherit Exception()
        member self.Value = value

    type Microsoft.FSharp.Control.Async with
        // efficient raise
        static member Raise (e : #exn) = Async.FromContinuations(fun (_,econt,_) -> econt e)
  
        static member Choice<'T>(tasks : seq<Async<'T option>>) : Async<'T option> =
            let wrap task =
                async {
                    let! res = task
                    match res with
                    | None -> return None
                    | Some r -> return! Async.Raise <| SuccessException r
                }

            async {
                try
                    do!
                        tasks
                        |> Seq.map wrap
                        |> Async.Parallel
                        |> Async.Ignore

                    return None
                with 
                | :? SuccessException<'T> as ex -> return Some ex.Value
            }

// example 1

let delay interval result =
    async {
        do! Async.Sleep interval
        return! async {
            printfn "returning %A after %d ms." result interval
            return result }
    }

[ delay 100 None ; delay 1000 (Some 1) ; delay 500 (Some 2) ] |> Async.Choice |> Async.RunSynchronously
                    
// example 2

/// parallel existential combinator
let exists (f : 'T -> Async<bool>) (ts : seq<'T>) : Async<bool> =
    let wrapper t = async { let! r = f t in return if r then Some () else None }
                
    async {
        let! r = ts |> Seq.map wrapper |> Async.Choice
        return r.IsSome
    }

#time
[1..500] |> Seq.exists (fun i -> Threading.Thread.Sleep 10; i = 500)
[1..500] |> exists (fun i -> async { let! _ = Async.Sleep 10 in return i = 500 }) |> Async.RunSynchronously
namespace System
Multiple items
type AutoOpenAttribute =
  inherit Attribute
  new : unit -> AutoOpenAttribute
  new : path:string -> AutoOpenAttribute
  member Path : string

Full name: Microsoft.FSharp.Core.AutoOpenAttribute

--------------------
new : unit -> AutoOpenAttribute
new : path:string -> AutoOpenAttribute
Multiple items
type private SuccessException<'T> =
  inherit Exception
  new : value:'T -> SuccessException<'T>
  member Value : 'T

Full name: Script.AsyncEx.SuccessException<_>

--------------------
private new : value:'T -> SuccessException<'T>
val value : 'T
Multiple items
type Exception =
  new : unit -> Exception + 2 overloads
  member Data : IDictionary
  member GetBaseException : unit -> Exception
  member GetObjectData : info:SerializationInfo * context:StreamingContext -> unit
  member GetType : unit -> Type
  member HelpLink : string with get, set
  member InnerException : Exception
  member Message : string
  member Source : string with get, set
  member StackTrace : string
  ...

Full name: System.Exception

--------------------
Exception() : unit
Exception(message: string) : unit
Exception(message: string, innerException: exn) : unit
Exception(info: Runtime.Serialization.SerializationInfo, context: Runtime.Serialization.StreamingContext) : unit
val self : SuccessException<'T>
member private SuccessException.Value : 'T

Full name: Script.AsyncEx.SuccessException`1.Value
namespace Microsoft
namespace Microsoft.FSharp
namespace Microsoft.FSharp.Control
Multiple items
type Async<'T>

Full name: Microsoft.FSharp.Control.Async<_>

--------------------
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
static member Async.Raise : e:#exn -> Async<'b>

Full name: Script.AsyncEx.Raise
val e : #exn
type exn = Exception

Full name: Microsoft.FSharp.Core.exn
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) * (OperationCanceledException -> unit) -> unit) -> Async<'T>
val econt : (exn -> unit)
Multiple items
static member Async.Choice : tasks:seq<Async<'T option>> -> Async<'T option>

Full name: Script.AsyncEx.Choice

--------------------
type Choice<'T1,'T2> =
  | Choice1Of2 of 'T1
  | Choice2Of2 of 'T2

Full name: Microsoft.FSharp.Core.Choice<_,_>

--------------------
type Choice<'T1,'T2,'T3> =
  | Choice1Of3 of 'T1
  | Choice2Of3 of 'T2
  | Choice3Of3 of 'T3

Full name: Microsoft.FSharp.Core.Choice<_,_,_>

--------------------
type Choice<'T1,'T2,'T3,'T4> =
  | Choice1Of4 of 'T1
  | Choice2Of4 of 'T2
  | Choice3Of4 of 'T3
  | Choice4Of4 of 'T4

Full name: Microsoft.FSharp.Core.Choice<_,_,_,_>

--------------------
type Choice<'T1,'T2,'T3,'T4,'T5> =
  | Choice1Of5 of 'T1
  | Choice2Of5 of 'T2
  | Choice3Of5 of 'T3
  | Choice4Of5 of 'T4
  | Choice5Of5 of 'T5

Full name: Microsoft.FSharp.Core.Choice<_,_,_,_,_>

--------------------
type Choice<'T1,'T2,'T3,'T4,'T5,'T6> =
  | Choice1Of6 of 'T1
  | Choice2Of6 of 'T2
  | Choice3Of6 of 'T3
  | Choice4Of6 of 'T4
  | Choice5Of6 of 'T5
  | Choice6Of6 of 'T6

Full name: Microsoft.FSharp.Core.Choice<_,_,_,_,_,_>

--------------------
type Choice<'T1,'T2,'T3,'T4,'T5,'T6,'T7> =
  | Choice1Of7 of 'T1
  | Choice2Of7 of 'T2
  | Choice3Of7 of 'T3
  | Choice4Of7 of 'T4
  | Choice5Of7 of 'T5
  | Choice6Of7 of 'T6
  | Choice7Of7 of 'T7

Full name: Microsoft.FSharp.Core.Choice<_,_,_,_,_,_,_>
val tasks : seq<Async<'T option>>
Multiple items
val seq : sequence:seq<'T> -> seq<'T>

Full name: Microsoft.FSharp.Core.Operators.seq

--------------------
type seq<'T> = Collections.Generic.IEnumerable<'T>

Full name: Microsoft.FSharp.Collections.seq<_>
type 'T option = Option<'T>

Full name: Microsoft.FSharp.Core.option<_>
val wrap : (Async<'a option> -> Async<'b option>)
val task : Async<'a option>
val async : AsyncBuilder

Full name: Microsoft.FSharp.Core.ExtraTopLevelOperators.async
val res : 'a option
union case Option.None: Option<'T>
union case Option.Some: Value: 'T -> Option<'T>
val r : 'a
static member Async.Raise : e:#exn -> Async<'b>
module Seq

from Microsoft.FSharp.Collections
val map : mapping:('T -> 'U) -> source:seq<'T> -> seq<'U>

Full name: Microsoft.FSharp.Collections.Seq.map
static member Async.Parallel : computations:seq<Async<'T>> -> Async<'T []>
static member Async.Ignore : computation:Async<'T> -> Async<unit>
val ex : SuccessException<'T>
property SuccessException.Value: 'T
val delay : interval:int -> result:'a -> Async<'a>

Full name: Script.delay
val interval : int
val result : 'a
static member Async.Sleep : millisecondsDueTime:int -> Async<unit>
val printfn : format:Printf.TextWriterFormat<'T> -> 'T

Full name: Microsoft.FSharp.Core.ExtraTopLevelOperators.printfn
static member Async.Choice : tasks:seq<Async<'T option>> -> Async<'T option>
static member Async.RunSynchronously : computation:Async<'T> * ?timeout:int * ?cancellationToken:Threading.CancellationToken -> 'T
val exists : f:('T -> Async<bool>) -> ts:seq<'T> -> Async<bool>

Full name: Script.exists


 parallel existential combinator
val f : ('T -> Async<bool>)
type bool = Boolean

Full name: Microsoft.FSharp.Core.bool
val ts : seq<'T>
val wrapper : ('T -> Async<unit option>)
val t : 'T
val r : bool
val r : unit option
property Option.IsSome: bool
val exists : predicate:('T -> bool) -> source:seq<'T> -> bool

Full name: Microsoft.FSharp.Collections.Seq.exists
val i : int
namespace System.Threading
Multiple items
type Thread =
  inherit CriticalFinalizerObject
  new : start:ThreadStart -> Thread + 3 overloads
  member Abort : unit -> unit + 1 overload
  member ApartmentState : ApartmentState with get, set
  member CurrentCulture : CultureInfo with get, set
  member CurrentUICulture : CultureInfo with get, set
  member DisableComObjectEagerCleanup : unit -> unit
  member ExecutionContext : ExecutionContext
  member GetApartmentState : unit -> ApartmentState
  member GetCompressedStack : unit -> CompressedStack
  member GetHashCode : unit -> int
  ...

Full name: System.Threading.Thread

--------------------
Threading.Thread(start: Threading.ThreadStart) : unit
Threading.Thread(start: Threading.ParameterizedThreadStart) : unit
Threading.Thread(start: Threading.ThreadStart, maxStackSize: int) : unit
Threading.Thread(start: Threading.ParameterizedThreadStart, maxStackSize: int) : unit
Threading.Thread.Sleep(timeout: TimeSpan) : unit
Threading.Thread.Sleep(millisecondsTimeout: int) : unit

More information

Link:http://fssnip.net/dN
Posted:4 years ago
Author:Nick Palladinos
Tags: async , choice , non-determinism