Rash thoughts about .NET, C#, F# and Dynamics NAV.

module RxExtensions.Observable

 

open System.Linq

open System

open System.Threading

open System.Windows.Threading

 

type ‘a observable = IObservable<‘a>

type ‘a observer = IObserver<‘a>

 

/// converts a lambda in a System.Action

let asAction f = new System.Action(f)

 

/// System.Action whichs does nothing

let doNothing = asAction (fun () -> ())

 

/// Creates an observer

let createObserver next error completed =

  {new System.IObserver<_> with

      member this.OnCompleted() = completed()

      member this.OnError(e) = error e

      member this.OnNext(args) = next args}

 

/// Creates a new observable

let create f =

  Observable.Create<_>(fun x ->

    f x

    doNothing)  

 

/// Creates a observable from a async

let ofAsync async =

  create

    (fun obs ->

       Async.StartWithContinuations

         (async,obs.OnNext,obs.OnError,obs.OnError))

 

/// Gets a dispatcher Schdeuler for the current dispatcher

let getDispatcherScheduler _ =

  new DispatcherScheduler(Dispatcher.CurrentDispatcher)

 

/// Generates an observable from an IEvent

let fromEvent (event:IEvent<_,_>) = create (fun x -> event.Add x.OnNext)

 

/// Generates an empty observable

let empty<‘a> = Observable.Empty<‘a>()

 

/// Takes the head of the elements

let head = Observable.First

 

/// Merges the two observables

let mergeWith obs1 obs2 = Observable.Merge(obs2, obs1)

 

/// Merges all observables

let mergeAll (observables:IObservable<IObservable<‘a>>) =

  Observable.Merge observables

 

/// Merges all observables

let merge (observables:(IObservable<‘a>) seq) =

  Observable.Merge observables

 

/// Creates a range as an observable

let range start count = Observable.Range(start, count)

 

/// Converts a seq in an observable

let toObservable (seq: ‘a seq) = Observable.ToObservable seq

 

/// Converts a observable in a seq

let toEnumerable = Observable.ToEnumerable

 

/// Subscribes to the Observable with all 3 callbacks

let subscribeComplete next error completed (observable: ‘a observable) =

   observable.Subscribe(

     (fun x -> next x),

     (fun e -> error e),

     (fun () -> completed()))

 

/// Subscribes to the Observable with a

/// next and an error-function

let subscribeWithError next error observable =

  subscribeComplete next error (fun () -> ()) observable

 

/// Subscribes to the Observable with just a next-function

let subscribe next observable =

  subscribeWithError next ignore observable

 

/// throttles the observable for the given interval

let throttle interval observable =

  Observable.Throttle(observable,interval)   

 

/// throttles the observable scheduled on the current dispatcher

let throttleOnCurrentDispatcher interval observable =

  Observable.Throttle(

     observable,getDispatcherScheduler(),interval)

 

/// samples the observable at the given interval

let sample interval observable =

  Observable.Sample(observable,interval)   

 

/// samples the observable at the given interval

/// scheduled on the current dispatcher

let sampleOnCurrentDispatcher interval observable =

  Observable.Sample(

    observable,getDispatcherScheduler(),interval)

 

/// returns the observable sequence that reacts first.

let takeFirstOf2Reactions obs1 obs2 =

  Observable.Amb(obs1,obs2)

 

/// returns the observable sequence that reacts first.

let amb (obs: IObservable<‘a> seq) =

  Observable.Amb obs  

 

/// returns the observable sequence that reacts first.

let takeFirstReaction (obs: IObservable<‘a> seq) =

  Observable.Amb obs  

 

/// Matches when both observable sequences

/// have an available value.

let both obs1 obs2 = Observable.And(obs1,obs2)

 

/// Merges two observable sequences

/// into one observable sequence.

let zip obs1 obs2 =   

   Observable.Zip(obs1, obs2, Func<_,_,_>(fun a b -> a, b))

 

/// Merges two observable sequences into one observable sequence

/// whenever one of the observable sequences has a new value.

///    ==> More results than zip

let combineLatest obs1 obs2 =   

   Observable.CombineLatest(

     obs1, obs2, Func<_,_,_>(fun a b -> a, b))    

 

/// Concats the two observables to one observable

let concat observable =

  Observable.SelectMany(

    observable,

    Func<_,_>(fun (x:IObservable<‘a>) -> x))

 

/// maps the given observable with the given function

let map f observable =

  Observable.Select(observable,Func<_,_>(f))  

 

/// maps the given observable with the given function

let mapi f observable =

  Observable.Select(observable,Func<_,_,_>(fun x i ->f i x))  

 

/// Filters all elements where the given predicate is satified

let filter f observable =

  Observable.Where(observable, Func<_,_>(f))

 

/// Splits the observable into two observables

/// Containing the elements for which the predicate returns

/// true and false respectively

let partition predicate observable =

  filter predicate observable,

  filter (predicate >> not) observable

 

/// Skips n elements

let skip n observable = Observable.Skip(observable, n)

 

/// Skips elements while the predicate is satisfied

let skipWhile f observable =

  Observable.SkipWhile(observable, Func<_,_>(f))

 

/// Runs all observable sequences in parallel

/// and combines their first values.

let forkJoin (observables: (‘a observable) seq) =

  Observable.ForkJoin observables

 

/// Counts the elements

let length = Observable.Count

 

/// Takes n elements

let take n observable =

  Observable.Take(observable, n)  

 

/// Determines whether the given observable is empty 

let isEmpty observable = Observable.IsEmpty observable

 

/// Determines whether the given observable is not empty 

let isNotEmpty observable = not (Observable.IsEmpty observable)

 

/// Determines whether an observable sequence

/// contains a specified value

/// which satisfies the given predicate

let exists predicate observable =

  observable

    |> skipWhile (predicate >> not)

    |> isNotEmpty

 

/// Continues an observable sequence that is terminated

/// by an exception with the next observable sequence.

let catch (newObservable:IObservable<‘a>) failingObservable =

  Observable.Catch(failingObservable,newObservable) 

 

/// Takes elements while the predicate is satisfied

let takeWhile f observable =

  Observable.TakeWhile(observable, Func<_,_>(f))

 

/// Iterates through the observable

/// and performs the given side-effect

let perform f observable =

  Observable.Do(observable,fun x -> f x)

 

/// Invokes finallyAction after source observable

/// sequence terminates normally or by an exception.

let performFinally f observable =

  Observable.Finally(observable,fun _ -> f())

 

/// Folds the observable

let fold f seed observable =

  Observable.Aggregate(observable, seed, Func<_,_,_>(f))  

 

/// Retruns an observable from a async pattern 

let fromAsync beginF endF =

   Observable.FromAsyncPattern<_>(

     Func<_,_,_>(fun x y -> beginF(x,y)),

       (fun x -> endF x)).Invoke()

 

/// Runs all observable sequences in parallel

/// and combines their first values.

let subscribeAll next observables =

  observables |> Seq.map (subscribe next) |> Seq.toList     

 

type IObservable<‘a> with

  /// Subscribes to the Observable with just a next-function

  member this.Subscribe(next) =

    subscribe next this

 

  /// Subscribes to the Observable with a next

  /// and an error-function

  member this.Subscribe(next,error) =

    subscribeWithError next error this

 

  /// Subscribes to the Observable with all 3 callbacks

  member this.Subscribe(next,error,completed) =

    subscribeComplete next error completed this

 

open System.Net

 

type WebRequest with

  member this.GetRequestStreamAsync() =

    fromAsync

     this.BeginGetRequestStream

     this.EndGetRequestStream

 

  member this.GetResponseAsync() =

    fromAsync

      this.BeginGetResponse

      this.EndGetResponse

 

  member this.GetResponseStreamAsync() =

    fromAsync

      this.BeginGetRequestStream

      this.EndGetRequestStream

 

type Async<‘a> with

  member this.ToObservable() = ofAsync this

open System.Windows.Forms

 

let form = new Form(Visible=true, Text="Async dict",

                       TopMost=true)

let textBox1 =

  new TextBox(

    Location = new System.Drawing.Point(12, 12),

    Size = new System.Drawing.Size(260, 20))

form.Controls.Add textBox1

 

let resultsBox =

  new ListBox(

    Location = new System.Drawing.Point(13, 39),

    Size = new System.Drawing.Size(259, 211))

form.Controls.Add resultsBox

 

// create a list with common words

// this might be very large

let data =

  ["hell"; "Hello"; "Halle"; "Html";

      "Bonn"; "Bonjour"; "Steffen"] 

 

// create observable for text changes

let textChanged =

  textBox1.TextChanged

    |> Observable.map (fun _ -> textBox1.Text)

module Observable

 

/// A Observable base class which notifies

/// all observers in parallel 

type ‘a Observable() =

  let mutable observers = []

 

  /// Notifies all observers in parallel about the new value

  let notifyObservers f =

    observers

      |> Seq.map (fun (observer:IObserver<‘a>) –>

                         async { return f observer})

      |> Async.Parallel

      |> Async.RunSynchronously

      |> ignore

 

  interface IObservable<‘a> with

    member observable.Subscribe(observer)  =

      // subscribe observer

      observers <- observer :: observers

      // create Disposable to unsubscribe observer later

      {new IDisposable with

         member this.Dispose() =

            observers <-

                observers |> List.filter ((<>) observer)}

 

  /// Notifies all observers in parallel about the new value

  member observable.OnNext value =

   notifyObservers (fun observer -> observer.OnNext value)

 

  /// Notifies all observers in parallel about the error

  /// and finishes all observations

  member observable.OnError error =

    notifyObservers (fun observer -> observer.OnError error)

    observers <- []

 

  /// Notifies all observers in parallel about the completion

  /// and finishes all observations

  member observable.Completed =

    notifyObservers (fun observer -> observer.OnCompleted())

    observers <- [] 

let wordsObservable = new Observable.Observable<_>()

 

let findWords prefix =

  if prefix <> "" then

    let prefix’ = prefix.ToUpper()

    for word in data do

      if word.ToUpper().StartsWith(prefix’) then

        wordsObservable.OnNext (prefix,word)

// create observers

let clean =

  textChanged

    |> Observable.subscribe (fun _ -> resultsBox.Items.Clear())

 

let searchForWords =

  // Every time the text changes

  // we start our wordsObservable to push words

  textChanged

    |> Observable.subscribe (fun text -> findWords text)

 

let wordFound =

  // subscribe to the "word found"-event

  wordsObservable   

    |> Observable.subscribe

        (fun (_,word) -> resultsBox.Items.Add word |> ignore)