F# in Silverlight

Over the last couple years, there has been an explosion of interest in Silverlight.  As a .NET-based runtime, it is possible to compile Silverlight applications with any .NET language, and we’ve seen a lot of F# developers using F# in Silverlight.  However, until recently this involved building an application using the desktop version of the F# runtime, which could result in some pitfalls and mixed levels of success.

With the recent F# May CTP though, we now provide a Silverlight version of the F# runtime, FSharp.Core.dll, along with the F# release.  This enables building truly first-class Silverlight components using F#.

To make this easier, I’ve posted some Silverlight F# project templates and samples on Code Gallery. 

Download

F# Templates and Samples for Silverlight

Templates

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Samples

L-Systems

Lindenmayer Systems are an interesting way of generating a variety of fractals using a simple set of rewrite rules.  Check out the fascinating book The Algorithmic Beauty of Plants for details.  The Silverlight application below uses an L-System rewriter and rendered written in F#.

  • F, G, A, B are drawn as a move forward.
  • + is a turn right.
  • - is a turn right.
  • X, Yand anything else is skipped during rendering.

Launch the L-System demo 

 open System.Windows
open System.Windows.Shapes

let rec internal applyRulesInOrder rules c =
    match rules with
    | [] -> string c
    | rule::rules' -> match rule c with | None -> applyRulesInOrder rules' c
        | Some result -> result

let internal step rules current =
     current
     |> String.collect (applyRulesInOrder rules)

let internal rotate (x,y) theta =
    let x' = x * cos theta - y * sin theta
    let y' = x * sin theta + y * cos theta
    (x',y')

let rec internal render (x,y) (dx,dy) angle points system =
    match system with | [] -> (x,-y)::points
    | 'A'::system' | 'B'::system' | 'F'::system' | 'G'::system' -> let x',y' = x+dx,y+dy
        render (x',y') (dx,dy) angle ((x,-y)::points)  system'
    | '+'::system' -> let (dx',dy') = rotate (dx,dy) angle
        render (x,y) (dx',dy') angle points system'
    | '-'::system' -> let (dx',dy') = rotate (dx,dy) (-angle)
        render (x,y) (dx',dy') angle points system'
    | _::system' -> render (x,y) (dx,dy) angle points system' let rec internal applyN f n x =
    if n = 0 then x
    else f (applyN f (n-1) x)

let internal normalize points =
    let minX = points |> Seq.map (fun (x,_) -> x) |> Seq.min
    let minY = points |> Seq.map (fun (_,y) -> y) |> Seq.min
    points |> List.map (fun (x,y) -> new Point(x-minX, y-minY)) type LSystem(rulesString:string, start:string, angle:int, stepSize:int, n:int) =
    let expanded,isError =
        try let rules =
                rulesString.Split([|"\r";"\n"|], System.StringSplitOptions.RemoveEmptyEntries)
                |> Array.map (fun line -> line.Split([|"->"|], System.StringSplitOptions.RemoveEmptyEntries))
                |> Array.map (fun fromAndTo -> (fromAndTo.[0].[0], fromAndTo.[1]))
            let ruleFunctions = [ for (c, s) in rules -> fun x -> if x = c then Some s else None]
            applyN (step ruleFunctions) n start, false with | e -> "", true member this.Render(polyline : Polyline) =
        let points = render (0.0,0.0) (float stepSize,0.0) (float angle * System.Math.PI / 180.0) [] (List.ofSeq expanded)
        for pt in normalize points do polyline.Points.Add(pt)
        isError

        

Console Control

A resuable Silverlight control providing a console emulation. The control exposes input and ouput streams akin to those on the System.Console class. Could be used to provide console input and output as part of a Silverlight application, or as a way to convert Windows Console apps to Silverlight apps.

This samples hooks the Console up to a simple echo loop.

Launch the Console Control

 namespace System.Windows.Controls

open System
open System.IO
open System.Windows
open System.Windows.Controls
open System.Windows.Input
open SilverlightContrib.Utilities.ClipboardHelper
open System.Text

// A shared base implementation of Stream for 
// use by the console input and output streams
[<AbstractClass>] type private ConsoleStream(isRead) = 
    inherit Stream()
    override this.CanRead = isRead
    override this.CanWrite = not isRead
    override this.CanSeek = false override this.Position
        with get() = raise (new NotSupportedException("Console stream does not have a position"))
        and set(v) = raise (new NotSupportedException("Console stream does not have a position"))
    override this.Length = raise (new NotSupportedException("Console stream does not have a length"))
    override this.Flush() = ()
    override this.Seek(offset, origin) = raise (new NotSupportedException("Console stream cannot seek"))
    override this.SetLength(v) = raise (new NotSupportedException("Console stream does not have a length")) 

/// A control representing a Console window 
/// Provides an InputStream and OutputStream 
/// for reading an writing character input. 
/// Also supports copy/paste on some browsers
type SilverlightConsole() as self = 
    inherit TextBox()

    // The queue of user input which has been collected by the 
 // console, but not yet read from the input stream 
 let readQueue = new System.Collections.Generic.Queue<int>()

    // A stream that reads characters from user input 
 let inputStream = 
        { new ConsoleStream(true) with override this.Write(buffer,offset,count) = 
                raise (new NotSupportedException("Cannot write from Console input stream"))
            override this.Read(buffer,offset,count) = 
                do System.Diagnostics.Debug.WriteLine("Starting to read {0} bytes", count)
                let rec waitForAtLeastOneByte() =
                    let shouldSleep = ref true let ret = ref [||]
                    lock readQueue  (fun () -> shouldSleep := readQueue.Count < 1
                        if not !shouldSleep then let lengthToRead = min readQueue.Count count
                            ret := Array.init lengthToRead (fun i -> byte (readQueue.Dequeue())))
                    if !shouldSleep
                    then System.Threading.Thread.Sleep(100); waitForAtLeastOneByte()
                    else !ret
                let bytes = waitForAtLeastOneByte()
                System.Array.Copy(bytes, 0, buffer, offset, bytes.Length)
                do System.Diagnostics.Debug.WriteLine("Finished reading {0} bytes", bytes.Length)
                bytes.Length
        }

    // A stream that sends character output onto the console screen 
 let outputStream =
        { new ConsoleStream(false) with override this.Read(buffer,offset,count) = 
                raise (new NotSupportedException("Cannot read from Console output stream"))
            override this.Write(buffer,offset,count) = 
                let isDelete = offset < 0
                let newText =
                     if isDelete
                     then "" else UnicodeEncoding.UTF8.GetString(buffer, offset, count)
                let _ = self.Dispatcher.BeginInvoke(fun () -> if isDelete then if self.Text.Length >= count then self.Text <- self.Text.Substring(0, self.Text.Length - count)
                    else do self.Text <- self.Text + newText
                    do self.SelectionStart <- self.Text.Length
                    do self.SelectionLength <- 0)
                ()
        }

    let shiftNumbers = [|')';'!';'@';'#';'$';'%';'^';'&';'*';'('|]
    let currentInputLine = new System.Collections.Generic.List<int>()

    // Handles key down events 
 // Processes the pressed key and turns it into console input 
 // Also echos the pressed key to the console 
 let keyDownHandler(keyArgs : KeyEventArgs) =
        try do keyArgs.Handled <- true let shiftDown = Keyboard.Modifiers &&& ModifierKeys.Shift <> (enum 0)
            let ctrlDown = Keyboard.Modifiers &&& ModifierKeys.Control <> (enum 0)
            let p = keyArgs.PlatformKeyCode
            if ctrlDown || keyArgs.Key = Key.Ctrl then if keyArgs.Key = Key.V then lock currentInputLine (fun () -> let clipboard = new ClipboardHelper()
                        let fromClipboard = clipboard.GetData()
                        for c in fromClipboard do do currentInputLine.Add(int c)
                            outputStream.WriteByte(byte c)
                            if c = '\n' then for i in currentInputLine do do System.Diagnostics.Debug.WriteLine("Enqueued {0}", char i)
                                    do readQueue.Enqueue(i)
                                do currentInputLine.Clear()
                    )
                elif keyArgs.Key = Key.C then let text = self.SelectedText
                    let clipboard = new ClipboardHelper()
                    clipboard.SetData(text)
            else System.Diagnostics.Debug.WriteLine("Got key {0} {1} {2}", p, char p, keyArgs.Key)
                let ascii =
                    match p with | n when n >= 65 && n <= 90 -> if shiftDown then p else p+32
                    | n when n >= 48 && n <= 57 -> if shiftDown then int shiftNumbers.[p-48] else p
                    | 8 -> 8 
 // backspace 
                    | 13 -> int '\n' 
                    | 32 -> int ' ' 
                    | 186 -> if shiftDown then int ':' else int ';' 
                    | 187 -> if shiftDown then int '+' else int '=' 
                    | 188 -> if shiftDown then int '<' else int ',' 
                    | 189 -> if shiftDown then int '_' else int '-' 
                    | 190 -> if shiftDown then int '>' else int '.' 
                    | 191 -> if shiftDown then int '?' else int '/' 
                    | 192 -> if shiftDown then int '~' else int '`' 
                    | 219 -> if shiftDown then int '{' else int '[' 
                    | 220 -> if shiftDown then int '|' else int '\\' 
                    | 221 -> if shiftDown then int '}' else int ']' 
                    | 222 -> if shiftDown then int '\"' else int '\'' 
                    | _ -> -1
                if ascii = 8 then lock currentInputLine (fun () -> if currentInputLine.Count > 0 then currentInputLine.RemoveAt(currentInputLine.Count - 1)
                        outputStream.Write([||], -1, 1)
                    )
                elif ascii > 0 then lock currentInputLine (fun () -> do currentInputLine.Add(ascii)
                        outputStream.WriteByte(byte ascii)
                    )
                if ascii = int '\n' then lock currentInputLine (fun () -> for i in currentInputLine do do System.Diagnostics.Debug.WriteLine("Enqueued {0}", char i)
                            if i = 10 then do readQueue.Enqueue(13)
                            do readQueue.Enqueue(i)
                        do currentInputLine.Clear())
                do self.SelectionStart <- self.Text.Length
                do self.SelectionLength <- 0
        with | e -> System.Diagnostics.Debug.WriteLine(e)

    // Lazily initialized StreamReader/StreamWriter 
 let outReader = lazy (new System.IO.StreamWriter(outputStream, Encoding.UTF8, 256, AutoFlush=true))
    let inReader = lazy (new System.IO.StreamReader(inputStream, Encoding.UTF8, false, 256))

    // Manually handle the Return key so we can accept newlines 
 do self.AcceptsReturn <- true 
 // Make sure a vertical scrollbar appears when needed 
 do self.VerticalScrollBarVisibility <- ScrollBarVisibility.Auto
    // Make the control read-only so that users cannot move the cusor or change the contents 
 // Unfortunatley, this also greys it out - ideally we could seperate theese two. 
 do self.IsReadOnly <- true 
 // Hookup the keyDownHandler 
 do self.KeyDown.Add(keyDownHandler)

    /// The raw input stream for the Console 
 member this.InputStream = inputStream :> Stream
    /// The raw ouput stream for the Console 
 member this.OutputStream = outputStream :> Stream

    /// A StreamWriter for writing to the Console 
 member this.Out = outReader.Value
    /// A StreamReader for reading from the Console 
 member this.In = inReader.Value

Summary

Try out F# with Silverlight using the F# May CTP and the F# for Silverlight templates.