Coding in a functional language requires more than simply knowing the syntax of that language. You can write a for loop in F# as easily as you can in C#, but you're missing out on the functional aspects of F# (and C# for that matter). We'll do an introduction to the language features of F# and how to unit test but more importantly we'll write some code with a functional mindset and discuss where and why you would want to use F# in your existing projects.

1. Thinking in F#
Mike Clement
@mdclement
mike@softwareontheside.com
http://blog.softwareontheside.com

2. XP Simple Design
•Passes all tests
•Clear, expressive, consistent
•No duplication
•Minimal

3. FizzBuzz
• If multiple of 3, get “Fizz”
• If multiple of 5, get “Buzz”
• If not, return input int as string
• Rules are in order

4. FizzBuzz Code

5. Currying/Partial function application
let Multiples divisor result x s = if x % divisor =
0 then s + result else s
let Fizzy = Multiples 3 "Fizz"
val Multiples : divisor:int -> result:string ->
x:int -> s:string -> string
val Fizzy : (int -> string -> string)
let Fizzy x s = if x % 3 = 0 then s + "Fizz" else s

6. Bowling Game Kata
The game consists of 10 frames as shown above. In each frame the player has two
opportunities to knock down 10 pins. The score for the frame is the total number of pins
knocked down, plus bonuses for strikes and spares.
A spare is when the player knocks down all 10 pins in two tries. The bonus for that frame is
the number of pins knocked down by the next roll. So in frame 3 above, the score is 10 (the
total number knocked down) plus a bonus of 5 (the number of pins knocked down on the
next roll.)
A strike is when the player knocks down all 10 pins on his first try. The bonus for that frame
is the value of the next two balls rolled.
In the tenth frame a player who rolls a spare or strike is allowed to roll the extra balls to
complete the frame. However no more than three balls can be rolled in tenth frame.

7. Bowling Game – The OO Way

8. Bowling Game
How do we get more functional?

9. Lists
[1, 2, 3, 4]
Head
Tail

10. Lists
[1, 2, 3, 4].Head = 1
[1, 2, 3, 4].Tail = [2, 3, 4]
[1, 2, 3, 4].Tail.Tail = [3, 4]

11. F# Resources
• http://en.wikibooks.org/wiki/F_Sharp_Programming
• F# for C# Developers by Tao Liu
• http://www.tryfsharp.org/
• https://github.com/ChrisMarinos/FSharpKoans

12. Mike Clement
• @mdclement
• mike@softwareontheside.com
• http://blog.softwareontheside.com
• https://github.com/mdclement
• http://agilecodegames.com
• Utah Software Craftsmanship
• http://utahsc.org
• @utahsc
• We meet the first Wednesday at SLCC