As presented at Prairie Dev Con 2014 in Winnipeg, Manitoba on Monday, April 7, 2014

1. Get Functional on the CLR:
Intro to Functional Programming with
F#
David Alpert | @davidalpert | http://about.me/davidalpert

2. Learning Goals
• Disambiguate functional programming
• Demystify F# and F# syntax
• Demonstrate .NET interoperability
• Experiment with F# syntax
• Create a new F# library project
• Write basic functions and data structures in F#
• Call F# from C#
So that you will be able to:

3. Put yourself in “I have no idea
what I’m doing” situations more
often. Your growth will be
exponential. - @derekbailey
https://twitter.com/derickbailey/status/452832022860292096

4. Woody Zuill
“Question Everything – put
special focus on our deepest
held beliefs. What we trust most
hides our biggest problems.”
Agile Maxim #2
http://zuill.us/WoodyZuill/2012/09/16/the-8-agile-maxims-of-woody-zuill/

5. We are addicted to complexity
We are addicted to
complexity

6. We are addicted to accidental
complexity
We are addicted to
accidental complexity

7. We are addicted to manipulating
state
We are addicted to
manipulating state

8. #noManipulatingState is like
#noDefects or #NoEstimates
#noManipulatingState
is like
#noDefects
or
#noEstimates

9. What is Functional Programming?
It is programming... with functions!
• Pure – Referentially Transparent
• First Class and Higher-Order functions
• Partial application & Currying

10. What is Functional Programming?
(function ($) {
$(document).ready(function () {
$('dt').click(function (ev) {
// do something interesting
});
function doSomethingElse(ev) {
// something else again
}
$('a').click(doSomethingElse);
});
})(jQuery);
Func<int, bool> isEven = x => x%2 == 0;
public static MvcHtmlString LabelFor<TModel, TValue>(
this HtmlHelper<TModel> html,
Expression<Func<TModel, TValue>> expression)
{
// ...
}
var someString = @Html.TextBoxFor(model => model.Rating)

11. Why F#?
• Concise
• Convenient
• Correctness
• Concurrency
• Complete
Concise
Convenient
Correctness
Concurrency
Complete

12. The “Billion Dollar Mistake”
http://www.infoq.com/presentations/Null-References-The-Billion-Dollar-Mistake-Tony-Hoare
Sir Charles Antony Richard Hoare, commonly
known as Tony Hoare, is a British computer
scientist, probably best known for the
development in 1960, at age 26, of Quicksort.
He also developed Hoare logic, the formal
language Communicating Sequential Processes
(CSP), and inspired the Occam programming
language.
Tony Hoare introduced Null references in
ALGOL W back in 1965 “simply because it was
so easy to implement”, says Mr. Hoare. He talks
about that decision considering it “my billion-
dollar mistake”.

13. We are addicted to accidental
complexity
We are addicted to
accidental complexity

14. From C# syntax to F# syntax
C# F#
Curly braces denote scope Indentation (i.e. Whitespace) denotes scope
Brackets and commas in argument list No brackets or commas
// single line comment // single line comment
/* multi-line comment */ (* multi-line comment *)
Explicit return Implicit return (value of the last expression)
public int Add(int x, int y)
{
return x + y;
}
let add x y = x + y
IEnumerable<T> seq<‘T>
IList<T> ‘T list
Null None ( an Option value)

15. Some more F# syntax
Description Syntax Evaluates to
Declare a list (of int) [2; 3; 4] int list = [2; 3; 4]
Prepend to a list 1 :: [2; 3; 4] int list = [1; 2; 3; 4]
Contact two lists [0; 1] @ [2; 3; 4] int list = [0; 1; 2; 3; 4]
Declare a tuple of int (1, 2, 3) int * int * int = (1, 2, 3)
Declare an optional value let x = Some(1) val x : int option = Some 1
Declare a ‘null’ value Let z = None val z : 'a option
Pipe a list into a function
(like Linq’s Select)
[1; 2; 3]
|> (fun x -> x ^ 2) int list = [1; 4; 9]

16. Functional Type Notation
let add1 x = x + 1 int -> int
let add x y = x + y int -> int -> int

17. Basic List Functions
List.filter : ('T -> bool) -> 'T list -> 'T list
List.map : ('T -> 'U) -> 'T list -> 'U list
List.fold : ('State -> 'T -> 'State) -> 'State -> 'T list -> 'State
predicate items result
projection items result
accumulator items final
state
initial
state
+ new item = final
state
initial
state

18. Basic List Functions
predicateitemsresult
projectionitemsresult
items
final
state initial
state
accumulator
+ new item = final
state
initial
state
public static IEnumerable<TSource> Where<TSource>( this IEnumerable<TSource> source, Func<TSource, bool> predicate )
public static IEnumerable<TResult> Select<TSource, TResult>( this IEnumerable<TSource> source, Func<TSource, TResult> selector )
public static TAccumulate Aggregate<TSource, TAccumulate>( this IEnumerable<TSource> source,
TAccumulate seed,
Func<TAccumulate, TSource, TAccumulate> func )

19. Demo: Rapid Prototyping with FSI
• Rapid prototyping with the FSI REPL
and the F# Interactive Window
Demo:
Rapid Prototyping w/ FSI REPL
& the F# Interactive window

20. Demo: File -> New F# Project
• Create a new F# library project
• Create a new C# library project w/ Nunit
• Add references and test F# code from C#Demo:
File -> New F# Project

21. Demo: Other goodies
• Parsing with FParsec
(a parser-combinator approach)
• Strongly-typed Units of Measure
• Domain Modelling (i.e. Lightweight DDD)
• Automated browser testing with Canopy
Demo:
Other F# goodies

22. References & Resources
Get Functional on the CLR:
Intro to Functional Programming with
F#
David Alpert | @davidalpert | http://about.me/davidalpert
Reference
• http://en.wikipedia.org/wiki/Functional_programming
• http://fsharpforfunandprofit.com/why-use-fsharp/
• http://www.infoq.com/presentations/Null-References-The-Billion-Dollar-Mistake-Tony-Hoare
• http://www.tryfsharp.org/Create
• http://fsharpforfunandprofit.com/posts/fsharp-in-60-seconds/
• http://lostechies.com/jimmybogard/2008/08/12/enumeration-classes/
• http://research.microsoft.com/en-us/um/cambridge/projects/fsharp/manual/fsharp-component-design-
guidelines.pdf [ Component design guidelines ]
• http://visualstudiogallery.msdn.microsoft.com/07636c36-52be-4dce-9f2e-3c56b8329e33 [ depth colorizer ]
Examples
• http://www.quanttec.com/fparsec/ [ A parser-combinator library ]
• https://github.com/davidalpert/furlstrong [ F# based url parsing with FParsec ]
• http://nuggle.me/ [ DC Circuits in F# ]
• http://blogs.msdn.com/b/andrewkennedy/archive/2008/08/29/units-of-measure-in-f-part-one-introducing-
units.aspx [ Custom units of measure in F# ]
• http://www.slideshare.net/ScottWlaschin/ddd-with-fsharptypesystemlondonndc2013 [ DDD & F# Types ]
• http://lefthandedgoat.github.io/canopy/ [ Browser automation DSL with F# ]