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F# in action: playing functional Conway's game of life John Conway's game of life has become a playground for programmers using different languages and platforms. It inspired many coding dojos and code retreats because it touches various aspects of development from component design to performance testing. In this session we are going to take functional approach and play different variations of Conway's game of life using F#. The session starts with presentation of a traditional game implementation in C#, so we can later compare it with F# versions. Switching to F#, we will first write an implementation for a standard two-dimensional board, and then extend it to support asynchronous workflows, parallel tasks and even boards of arbitrary dimensions. Each implementation will be complemented with a set of tests using FsUnit framework, and graphical presentation of results will use Microsoft Chart Controls.
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Vagif Abilov
Playing functionalConway’s game of life
About myself
• Mail: [email protected]• Twitter: @ooobject• GitHub: object• BitBucket: object• Blog:
http://bloggingabout.net/blogs/vagif/default.aspx• Articles: http://www.codeproject.com
The source code for this presentation can be found at https://github.com/object/ConwayGame
Vagif Abilov
Playing functionalConway’s game of life
Conway’s game of life
• Invented in 1970 by the British mathematician John Conway
• Zero-player game, its evolution is fully determined by its initial state
• The universe of the Game of Life is an infinite two-dimensional orthogonal grid of square cells, each of which is in one of two possible states, alive or dead
Source: Wikipedia
Rules of Conway’s game of life
1. Any live cell with fewer than two live neighbours dies, as if caused by under-population.
2. Any live cell with two or three live neighbours lives on to the next generation.
3. Any live cell with more than three live neighbours dies, as if by overcrowding.
4. Any dead cell with exactly three live neighbours becomes a live cell, as if by reproduction.
Impelemening Conway’s game
How would you approach the implementation?
A small quiz: what names should we introduce?
• Classes• Class properties• Class methods• Structs• Enums
What people say on Twitter
“How is writing Java like writing classic Russian literature? You have to introduce 100 names before anything
can happen.”
@jamesiry
Speaking about Russian literature
Nightingales, a sigh, a whisperIn a shady nookAnd the lullaby in silverOf a lazy brook.…
• A short poem by Afanasy Fet (1850)• 12 lines, not a single verb
Checking other implementations
Source:http://www.codeproject.com/Articles/185208/Solving-Conway-s-Game-of-Life-using-State-Pattern
Implementation code metrics
• 5 classes (including 2 subclasses)• 5 properties• 5 methods• 316 lines of code• 64 effective lines of code (calculated using VS
code metrics)
Cell state definition
Discussion in comments about cell state definition
• Class (base class with 2 subclasses implementing State pattern)
• Enum (Dead, Alive)• Boolean
What would you choose?
Cell state choice consequence
• No matter what type you choose to represent cell state, you will need a cell property to hold it
• Having cells with different property values (Dead and Alive) encourages design where both types of cells are stored
• Storing cells with different states has negative impact on the scalability
• Moreover: it limits the solution to boards of fixed size
• Adding names add constraints!
Imperative languages lessons
• Symbol definition does not necessarily lead to clean code
• Names are opinionated, more names – more opinions
• More names – more constraints• Design patterns are often introduced to patch up
shortcomings in the language
Entering functional programming
Conway’s game of life is about transforming cell generations
What if we focus just on functional transformations?
Implementation plan
1. Classical game of life2. Multidimensional game of life3. Concurrent game of life4. Game of life visualization5. Surprise, surprise…
Classical game of life
Multidimensional game of life
Asynchronous game of life
Asynchronous burden
• Asynchronous support requires revision of API and its implementation
• It is common to offer two (significantly different) versions of API: one for synchronous and one for asynchronous execution
• Mutable nature of imperative languages require major changes if not complete rewrite of components to become thread-safe and support asynchronous or parallel execution
Asynchronous programming model
• Synchronous: – Execute (can be any verb, e.g. Read)
• Asynchronous:– BeginExecute (receives AsyncCallback, returns IAsyncResult)– EndExecute (receives IAsyncResult object)– <Callback> method (receives IAsyncResult)
• File IO example:– Read– BeginRead, EndRead, <Callback>
Benchmark results
Pattern size*
C# Linq F# F# Async F# PSeq
10** 0:00.183 0:00.357 0:00.320 0:00.570
25 0:00.428 0:00.315 0:00.157 0:00.196
50 0:06.034 0:04.064 0:01.512 0:01.231
100 1:25.162 1:06.429 0:27.428 0:31.270
* Pattern size N corresponds to a square N * N used to generate a pattern of N * N / 2 elements
** Pattern size 10 was used to warm up the text fixture
Game of life visualization
Time for surprises
Life in a tweet
Living with no sense of monad
Life in a tweet
• A great algorithm should fit in a tweet• If an algorithm does not fit in a tweet, it’s
overcomplicated• But to fit a great algorithm in a tweet you need a
great programming language• F# is a great programming language!
Life in a tweet
let f s g = g|>List.mapi(fun i x->match Seq.sumBy(fun o-> g.[abs((i+o)%(s*s))])[-1-s;-s;1-s;-1;1;-1+s;s;1+s]with 3-> 1|2->x|_->0)
• Written by Phil Trelfold (http://trelford.com/blog/post/140.aspx)
• 127 characters long
Song time!
Living With No Sense of Monads
Originally performed by Smokie with slightly different words
Living with no sense of monads
I first met Alice in a small bookstore,"What book, - I asked, - are you looking for?"And she said: "About monads."
I understood that's a key to her heart,I had no doubts that I was smart.It should be easy reading, an easy start...
Living with no sense of monads
But I still don't get this wisdom,It's really mystic wordI guess it has it's reasons,Someone gets it, but I don't.'Cos for twenty-four yearsI've been trying to understand the monads.
Living with no sense of monads
Twenty-four yearsJust waiting for a chance,I have to keep on reading, Maybe get a second glance,I will never get used to not understanding sense of monads
Living with no sense of monads
Grew up together,Went to the same class,And to be honest:I was better in mathThan Alice.
Living with no sense of monads
Too old for rock-n-roll - I'm forty four,Too young for monads - still have a hope.That the day will come When I let Alice know...
Living with no sense of monads
But I still don't get this wisdom,It's really mystic wordI guess it has it's reasons,Someone gets it, but I don't.'Cos for twenty-four yearsI've been trying to understand the monads.
(all together):Monads! What the f*ck is monads?!
Living with no sense of monads
Twenty-four yearsJust waiting for a chance,I have to keep on reading, Maybe get a second glance,I will never get used to not understanding sense of monads
Thank you!
• Mail: [email protected]• Twitter: @ooobject• GitHub: object• BitBucket: object• Blog:
http://bloggingabout.net/blogs/vagif/default.aspx• Articles: http://www.codeproject.com
The source code for this presentation can be found at https://github.com/object/ConwayGame
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