F# in Silverlight

F# in Silverlight

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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. 


F# Templates and Samples for Silverlight





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 =
     |> 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

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)


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


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

Leave a Comment
  • Please add 2 and 4 and type the answer here:
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  • That's a splendid idea! What about a LOGO implementation? I wished I had the time to do it.

    Anyway, well done and keep going.

  • Great FUN, F# and SL!



  • Great article, Luke!

    Looking forward to part 2:

    Hosting F# Interactive in Silverlight.


  • This is just so COOL!!! I was waiting for a long time to use SL in F#, Thanks a lot!!!! :)

  • Too bad silverlight didn't give anything back to the browser or the OS while it was thinking and thrashing -- it had to power-cycle my machine when trying a complex hex rendering. No broswer action, no ctrl-shift-esc, no ctrl-alt-del...

  • Hi,

    Nice examples.  Do you have any idea when we might see project templates for F# Silverlight libraries for Visual Studio 2010 beta 1?



  • Roly - We expect to include F# templates for Silverlight development along with Visual Studio 2010 Beta2.  For Beta1 though, we unfortunatley don't have a version of FSharp.Core.dll for Silverlight which ships with the release, so we can't easily provide an interim set of templates here, aside from those for VS2008, linked above.

  • No probs.  I'll wait for for beta 2!  Thanks again for the great examples - love the L-systems one.

  • This article's translated into Russian.

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