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Functional backoff/retry

Backoff/retry with injected mapping from call result to success criterion, and backoff times as a parameter. (New version with the backoff in the right place!)

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open System.Net

let rec Retry (f : unit -> 'T) (didSucceed : 'T -> bool) (timesMs : int list) =
   let rec retry times =
      match times with
      | [] ->
         f()
      | head::tail ->
         let result = f()
         if didSucceed result then
            result
         else
            async { do! Async.Sleep(head) } |> Async.RunSynchronously
            retry tail
   retry timesMs

let Demo1() =
   let rand = new System.Random()
   Retry (fun () -> rand.NextDouble()) (fun x -> x > 0.5) [1; 2; 4]

type DownloadResult = | Ok | NotOk

let Demo2() =
   use wc = new WebClient()
   Retry 
      (fun () -> 
         try
            printf "Downloading..."
            wc.DownloadFile("www.example.com", "file.txt")
            Ok
         with
         | _ -> NotOk)
      (fun result -> result = Ok)
      [1; 2; 4]
namespace System
namespace System.Net
val Retry : f:(unit -> 'T) -> didSucceed:('T -> bool) -> timesMs:int list -> 'T

Full name: Script.Retry
val f : (unit -> 'T)
type unit = Unit

Full name: Microsoft.FSharp.Core.unit
val didSucceed : ('T -> bool)
type bool = System.Boolean

Full name: Microsoft.FSharp.Core.bool
val timesMs : int list
Multiple items
val int : value:'T -> int (requires member op_Explicit)

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

--------------------
type int = int32

Full name: Microsoft.FSharp.Core.int

--------------------
type int<'Measure> = int

Full name: Microsoft.FSharp.Core.int<_>
type 'T list = List<'T>

Full name: Microsoft.FSharp.Collections.list<_>
val retry : (int list -> 'T)
val times : int list
val head : int
val tail : int list
val result : 'T
val async : AsyncBuilder

Full name: Microsoft.FSharp.Core.ExtraTopLevelOperators.async
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.Sleep : millisecondsDueTime:int -> Async<unit>
static member Async.RunSynchronously : computation:Async<'T> * ?timeout:int * ?cancellationToken:System.Threading.CancellationToken -> 'T
val Demo1 : unit -> float

Full name: Script.Demo1
val rand : System.Random
Multiple items
type Random =
  new : unit -> Random + 1 overload
  member Next : unit -> int + 2 overloads
  member NextBytes : buffer:byte[] -> unit
  member NextDouble : unit -> float

Full name: System.Random

--------------------
System.Random() : unit
System.Random(Seed: int) : unit
System.Random.NextDouble() : float
val x : float
type DownloadResult =
  | Ok
  | NotOk

Full name: Script.DownloadResult
union case DownloadResult.Ok: DownloadResult
union case DownloadResult.NotOk: DownloadResult
val Demo2 : unit -> DownloadResult

Full name: Script.Demo2
val wc : WebClient
Multiple items
type WebClient =
  inherit Component
  new : unit -> WebClient
  member BaseAddress : string with get, set
  member CachePolicy : RequestCachePolicy with get, set
  member CancelAsync : unit -> unit
  member Credentials : ICredentials with get, set
  member DownloadData : address:string -> byte[] + 1 overload
  member DownloadDataAsync : address:Uri -> unit + 1 overload
  member DownloadFile : address:string * fileName:string -> unit + 1 overload
  member DownloadFileAsync : address:Uri * fileName:string -> unit + 1 overload
  member DownloadString : address:string -> string + 1 overload
  ...

Full name: System.Net.WebClient

--------------------
WebClient() : unit
val printf : format:Printf.TextWriterFormat<'T> -> 'T

Full name: Microsoft.FSharp.Core.ExtraTopLevelOperators.printf
WebClient.DownloadFile(address: System.Uri, fileName: string) : unit
WebClient.DownloadFile(address: string, fileName: string) : unit
val result : DownloadResult

More information

Link:http://fssnip.net/re
Posted:2 years ago
Author:Kit Eason
Tags: retry