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Pacman Kata at Progressive F# Tutorials NYC 2013

I’m a bit of a Pacman fan so when I came across the Pacman Kata in the Kata Catalogue I was hooked:

Pacman finds himself in a grid filled with monsters. Will he be able to eat all the dots on the board before the monsters eat him?

Back in early 2012 we ran a Pacman Kata at the F#unctional Londoners meetup where you start with a maze and sprites and your task is to write a simple AI. After the event I extended the sample to run on Windows 8, Windows Phone as well as Silverlight and WPF, and somehow got a mention from Channel 9.

A few months back Neil Danson ported the sample to iOS, and over the last few weeks I’ve been playing with the HTML 5 canvas and have created a FunScript version too.

When Rich Minerich suggested a version for the Progressive F# Tutorials in New York I jumped at the chance, and teamed up with Mathias Brandewinder to create a fun session centred around Pacman:


Code samples from the session:

Test-driven Pacman

The session began with some good old unit tests:

let ``pacman should wrap from left to right beyond left extent`` () =
    let p = wrap { x = leftExtent-1; y =0 }
    Assert.AreEqual(rightExtent, p.x)

Followed by automated acceptance tests using TickSpec:

Scenario: Pacman eats dots
  When pacman eats a pac-dot
  Then he scores 10

Scenario: Pacman eats power pellets
  When pacman eats a power pellet
  Then he scores 50

In the sample the scenarios are automated using attribute based step definitions:

type Property = PacDot | PowerPellet

let [<When>] ``pacman eats a pac-dot`` () =
    properties <- PacDot::properties

let [<When>] ``pacman eats a power pellet`` () =
    properties <- PowerPellet::properties

let [<Then>] ``he scores (.*)`` (points:int) =
    let scored =
        properties |> List.sumBy (function
            | PacDot -> 10
            | PowerPellet -> 50
    Assert.AreEqual(points, scored)


Next up we looked at implementing keyboard controls, first with Mario and then Pacman, both in FunScript:

Pacman keys 

The controls can be composed from simple functions:

let left (dx,_) p = if dx = –1 then {p with x=p.x+dx} else p
let right (dx,_) p = if dx = 1 then {p with x=p.x+dx} else p
let up (_,dy) p = if dy = -1 then {p with y=p.y+dy} else p
let down (_,dy) p = if dy = 1 then {p with y=p.y+dy} else p

let step dir pacman = pacman |> left dir |> right dir |> up dir |> down dir


The grand finale was writing your own AI for the Ghosts (or Pacman) using an API designed by Mathias specifically for the session:

// Decision is based on current move, line of sight and possible moves
member this.Decide (current: Move) (lineOfSight: Sight) (choices: Move Set) =
    n <- n + 1
    let inSight (creatures:Creature list) =
        |> List.exists (function PacMan 0 -> true | _ -> false)

    let standard  () =
        let restricted =                 
            |> Set.filter (fun c -> not (c = backwards current))
        if (restricted |> Set.count > 0)
        then randomMove restricted
        else randomMove choices

    let home () =
        let s = lineOfSight
        let xs = [Up,s.Up; Down,s.Down; Left,s.Left; Right,s.Right]
        let x = 
            |> List.tryFind (fun (d,xs) ->
                xs |> List.exists (snd >> inSight)
        match x with
        | Some (d,_) -> d
        | None -> standard ()

    if (n / 500) % 2 = 0 then home ()
    else standard ()

The simple AI above switches the ghosts between homing in on Pacman and random moves every 500 frame updates (roughly every 8 seconds).

At the end we played off Mathias’s payoff function based Pacman AI against my simple Ghosts on the big screen which ended in a tie :)

Blue ghosts

In the more competitive Pacman session ran by Paulmichael Blasucci and Rich Minerich the final was between Jack Fox and Tyler Smith.

More fun

And there’s more fun to come, Rich Minerich will be running a Pacman competition at the Progressive F# Tutorials in London this year:

ProgFsharp London 2013

and there’s a Pacman Kata scheduled for November at the F#unctional Londoners meetup.

Walkie Scorchie

From the window at the office I’ve seen a series of futuristic buildings erected, first the Gherkin, then the Shard and now the Walkie Talkie:

London skyline 

The last one being recently been re-dubbed the Walkie Scorchie as it produces a supercharged solar ‘death ray’ that has burned holes in carpets, melted furniture and even the interior of a Jaguar parked nearby.

It feels almost reminiscent of the dystopian future portrayed in the cult film Idiocracy:

Idiocracy skyline

Though our current society is probably closer to the surveillance society of 1984 with the omnipresent Big Brother watching over you:

Big brother is watching you

The everyday software we work with is no less broken, or so Scott Hanselman concludes in everything's broken and nobody's upset.

Software is increasingly a world of broken windows where developers are more accustomed to working around issues than giving feedback, let alone tackling the root causes.

waiting for background operation to complete modal dialog 

Anyone else struggling with the cognitive dissonance of a modal dialog waiting for a background operation to complete?


I’ve been using XAML in it’s various guises off an on for over 5 years now. Over that time I’ve used WPF, Silverlight and Metro. It feels like little has changed in that time. It’s still probably the best thing out there for desktop app development but surely we could do better.


I’m still stuck editing views in XML, the poor man’s DSL. I, like the developers I know rarely use the designer view. When we do it frequently hangs and we’re left manually killing XDescProc.exe from task manager.

Data Binding

Data binding is central to XAML. With it you can easily bind a collection to a data grid and get sorting and filtering for free. But binding comes with a high performance cost and it’s stringly typed nature means you’re left finding binding errors in the output window at runtime.

Dynamically binding a view to a model would make more sense to me if I could edit the view at runtime, but you can’t, it’s compiled in.

Value Converters

If I want to transform a model value bound to the view to a different form I have to create a class that implements the IValueConverter interface then reference it as a static resource in the resources section. It has all the elegance of C++ header files. Achieving the same thing in ASP.Net is much simpler, you can just write inline some code in the view or call a function.


There’s a plethora of libraries and frameworks dedicated to working around this design decision, from the MVVM frameworks with LINQ expressions to PostSharp and attributes. The C# 5 compiler’s CallerMemberName attribute has finally brought some sanity to the situation. But I know many developers, including myself, have wasted countless hours dealing with it and trying to think of ways of subverting it.

Just about every view model class ends up inheriting from some ViewModelBase or ObservableObject class so that it can implement INotifyPropertyChanged.


It is often said that object-oriented programming is well suited to graphical user interfaces. Perhaps, but I start to have doubts when I see WPF’s Button class with 9 layers of inheritance and over 160 members.

Visual Studio 2010 introduced improved intellisense with substring search on members to partially work around this, but honestly I’d prefer to see buttons be closer to having content and a clicked event than their current diaspora of responsibilities.

Null Reference Exceptions

By far the most common error I see in C# applications is Null Reference Exceptions. Hardly a day goes by where yet another null check is added to the codebase. This needs to be fixed at the language level, functional-first languages like Scala and F# show it’s possible.

HTML5 & JavaScript

HTML 5 and JavaScript are now being pushed as an alternate environment for desktop development. JavaScript has come a long way performance and libraries wise and I like the HTML 5 Canvas model. However I’m not yet convinced how well this scales to multi-window applications that need to interact between processes.

Windows 8

I get that Metro style interfaces are good for tablets and touch, but for multi-window desktop applications it feels like a non-starter.


I’ve seen traders use 9 displays simultaneously, running a multitude of different apps from execution platforms and news services to Excel, Outlook and instant messengers.

To me Windows 8 appears to be consumer orientated release. I’m hoping the next version will bring something for the larger customer base of business users.


One person’s problem is another’s opportunity. Third party vendors like JetBrains are grasping the opportunity with both hands by patching flaws in Visual Studio and C# with tools like Resharper. They’re now starting to provide elastoplasts over XAML editing too. Jetbrains are not the only ones, Telerik and others are making hay selling themes and datagrids.


To temporarily workaround performance issues caused by the cost of the mouse handler events in one these products we were forced to throttle the number of system mouse events bubbling through the system.

Duct tape is a good short term solution, but surely at some point we should consider building a stronger foundation.


I would not give a fig for the simplicity this side of complexity, but I would give my life for the simplicity on the other side of complexity. - Oliver Wendell Holmes, Jr.

XAML is huge and bloated, WPF 4.5 Unleashed is 864 pages long, yet XAML’s focus on data binding makes it feel like a one-trick pony.

I think a modern desktop UI environment needs to cover a diverse range of product scenarios. There should be a low-level core that can be easily accessed with code for high performance features all the way up to a designer view for tacking databases on to views, and it should all interoperate seamlessly.

Sections of the development community are striving to bring simplicity to our environments. Language designers like Rich Hickey (Clojure) and Don Syme (F#) are bringing us simplicity at the language level. I’d love to see these thought processes applied to UI environments too.

To tackle the root causes of problems some times you need to stop continuously patching over the cracks, step back and take time to look at the big picture. To create Clojure Rich Hickey practised Hammock driven development. I’d love to see more of this kind of thoughtful design and less Mortgage driven development.

Tackling the root causes of complexity and defects in our software is not an easy choice, it requires investment and changes to the way we do things. But not changing is a choice too.

They live out their lives in this virtual reality as they would have around the turn of the 20th and 21st centuries. The time period was chosen because it is supposedly the pinnacle of human civilization. – Agent Smith

Must Java like languages and XML be considered the pinnacle of software development for time immemorial?

Generative Art

Last night I ran a free hands on Generative Art session to a full class room at Skills Matter for the F#unctional Londoners meetup group. We host a hands on programming sessions every month, next month we’ll return to the Machine Learning theme with Matt Moloney from the Tsunami IDE team.


I recently picked up Matt Pearson’s Generative Art book published by Manning, his examples use the Processing programming language which is loosely based on Java. For the hands on creative part we used F# and the SmallSharp library which has a similar feel but is limited to 2D.


SmallSharp is a small .Net library for drawing graphics, similar to Small Basic but aimed more at the "Sharp" languages C# and F#

Small Basic the good parts:

  • minimal IDE: you get intellisense, buttons for opening and saving files and a big run button (F5)
  • simple library: type GraphicsWindow and dot to start drawing shapes, no need worry about Single Threaded Apartments, data binding or XAML

Small Basic’s library is just about usable from C# and F# but relies on strings and implicit conversions to a variant type, where as SmallSharp’s API takes explicit typed arguments.

In F# with SmallSharp we can write:

GraphicsWindow.BrushColor <- red
for i in 0..5..200 do


Which draws concentric lines:



I found a nice piece on Deviant Art entitled Bubbles:


The task was to generate a similar work, starting with the following code:

Win.Background <- black
let rand = System.Random()
let colors = [red; green; blue; yellow]
for i = 1 to 200 do
    Win.Opacity <- rand.NextDouble() ** 3.0
    Win.FillColor <- colors.[rand.Next(colors.Length)]
    let x = rand.NextDouble() * Win.Width
    let y = rand.NextDouble() * Win.Height
    let r = 10.0 + rand.NextDouble() * 30.0

Here’s a monochrome from David Kowalski:


and an interesting Spiral effect from Rob Lyndon:

Spiral Galaxy


Following Atwood's Law:

any application that can be written in JavaScript, will eventually be written in JavaScript.

I created the same effect using the HTML5 Canvas, with the F# code being compiled to JavaScript by the FunScript library, which also gives typed access to JavaScript libraries.

module Program

open FunScript
open FunScript.TypeScript

type ts = Api<"../Typings/lib.d.ts">

let circle (ctx:ts.CanvasRenderingContext2D) (x,y,d,c) =
   let pi = ts.Math.PI
   ctx.arc(x, y, d, 0.0, pi * 2.0)
   ctx.fillStyle <- c

let inline str x = x.ToString()
let rgba (r,g,b) a = "rgba("+str r+","+str g+","+str b+","+str a+")";
let next n = ts.Math.random() * n
let from n = ts.Math.floor(next (float n)) |> int

let main() =
   let canvas = unbox<ts.HTMLCanvasElement>(ts.document.getElementById("canvas"))
   canvas.width <- 1000.
   canvas.height <- 500.
   let ctx = canvas.getContext("2d")
   // Set background
   ctx.fillStyle <- "rgb(0,0,0)"
   ctx.fillRect (0., 0., canvas.width, canvas.height);
   /// Circle colors
   let colors = [
   // Draw circles
   for i = 1 to 200 do
      let x = next canvas.width
      let y = next canvas.height
      let r = 10. + next 40.
      let a = next 1.
      let c = rgba (colors.[from colors.Length]) a
      circle ctx (x, y, r, c)


Turing Drawings

We finished up on drawing roulette with Turing drawings, made by random Turing machines:


I created an F# version a few weeks back which you can run in the Cloud Tsunami IDE.

Have fun!