A talk I gave to the Sydney Alt.NET group on Tuesday 30th June 2009 about some of the stuff I've learnt playing around with F#.

1. F#
What I’ve learnt so far
Mark Needham

2. What is F#?

3. Another language that
runs on the CLR

4. Interoperable with
other .NET languages

5. Functional...

6. ...but with Object
Oriented features too

7. Statically typed with type
inference

8. Why did I want to learn F#?

9. Different mindset

10. Immutability

11. Concurrency

12. How did I go about learning
F#?

15. Functions

16. Can live on their own

17. let add a b = a + b
http://intwoplacesatonce.com/?p=9

18. Type inference

19. let add a b = a + b
val add : int ‐> int ‐> int

20. let add (a:string) (b:string) = a + b
val add : string ‐> string ‐> string

21. Lots of ways to do the same thing

22. let withLinks (statuses:seq<TwitterStatus>) =
Seq.filter
(fun s ‐> s.Text.Contains("http"))
statuses

23. let withLinks (statuses:seq<TwitterStatus>) =
statuses |>
Seq.filter (fun s ‐> s.Text.Contains("http"))

24. Forward operator (|>)
('a ‐> ('a ‐> 'b) ‐> 'b)

25. let withLinks (statuses:seq<TwitterStatus>) =
Seq.filter (fun s ‐> hasLink s) statuses
let withLinks (statuses:seq<TwitterStatus>) =
statuses |> Seq.filter (fun s ‐> hasLink s)
let withLinks statuses =
statuses |> Seq.filter (fun (s:TwitterStatus) ‐> hasLink s)
let withLinks (statuses:seq<TwitterStatus>):seq<TwitterStatus> =
statuses |> Seq.filter (fun s ‐> hasLink s)
let withLinks : seq<TwitterStatus> ‐> seq<TwitterStatus> =
Seq.filter (fun s ‐> hasLink s)

26. Composing functions

27. let statuses = seq { yield new TwitterStatus() }
let sortedStatuses = Seq.sortBy
(fun (s:TwitterStatus) ‐> s.Id)
statuses
let firstStatus = Seq.hd sortedStatuses

28. seq { yield new TwitterStatus() }
|> Seq.sortBy (fun (s:TwitterStatus) ‐> s.Id)
|> Seq.hd

29. Functions are cool but
lack structure

30. Refactoring to objects

31. type Tweets = {
TwitterStatuses:seq<TwitterStatus>
}

32. let myTweets = {
TwitterStatuses = TwitterService.GetStatuses 100
}

33. let withLinks (statuses:seq<TwitterStatus>) =
statuses |> Seq.filter (fun s ‐> s.Text.Contains("http"))
let print (statuses:seq<TwitterStatus>) =
for s in statuses do
printfn "[%s] %s" s.User.ScreenName status.Text
type Tweets with
member t.print() = print t.TwitterStatuses
member t.withLinks() =
{
TwitterStatuses = withLinks t.TwitterStatuses
}

34. Leads to simpler/easier to
understand code

35. Helped by unit testing

36. xUnit.NET

37. [<Fact>]
let should_recognise_message_with_link_as_a_link () =
let messageWithLink =
(new MessageBuilder(message = "http://www.google.com")).Build()
Assert.True(messageWithLink |> hasLink)

38. type MessageBuilder(?message:string, ?user:string) =
let buildMessage message user =
new TwitterStatus(
Text = message,
User = new TwitterUser(ScreenName = user)
)
member mb.Build() =
buildMessage (if message.IsSome
then message.Value
else "")
(if user.IsSome
then user.Value
else "")

39. [<Fact>]
let should_not_show_any_tweets_by_me () =
let messageByMe =
(new MessageBuilder(message = "",
user = "markhneedham")).Build()
let tweets = seq { yield messageByMe;
yield messageByMe;
yield messageByMe }
let tweetsExcludingMe = tweets |> excludeSelf
Assert.Equal(0, tweetsExcludingMe |> Seq.length)

40. Still doing all the processing at
the end

41. Asynchronous Workflows

42. “Perform a computation in a
background thread without
blocking execution on current
thread”

43. Couch
Twitter DB
Write to
Tweets with
Tweet
Main links
Processor
Processor
Has link?

44. What am I learning next?

45. Programming in a more
functional way

46. Loops -> List functions/recursive
Objects -> ADTs
Classes -> Modules/Signatures/Functors

47. Quotations

48. Where can you learn more?

49. Books

50. Hub FS (http://cs.hubfs.net)
Chris Smith’s Blog
(http://blogs.msdn.com/chrsmith/)
Wes Dyer’s Blog
(http://blogs.msdn.com/wesdyer/)
On the web
Tomas Petricek’s Blog
Matthew Podwysocki’s Blog (http://tomasp.net/blog/)
(http://weblogs.asp.net/Podwysocki/)
Robert Pickering’s Wiki
(http://www.strangelights.com/FSharp/Wiki/)

51. Mark Needham
mneedham@thoughtworks.com
Blog: http://www.markhneedham.com/blog
Twitter: markhneedham