get functional on the clr: intro to functional programming with f#
DESCRIPTION
As presented at Prairie Dev Con 2014 in Winnipeg, Manitoba on Monday, April 7, 2014TRANSCRIPT
Get Functional on the CLR: Intro to Functional Programming with
F#
David Alpert | @davidalpert | http://about.me/davidalpert
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:
Put yourself in “I have no idea what I’m doing” situations more
often. Your growth will be exponential. - @derekbailey
htt
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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/
We are addicted to complexity
We are addicted to complexity
We are addicted to accidental complexity
We are addicted to accidental complexity
We are addicted to manipulating state
We are addicted to manipulating state
#noManipulatingState is like #noDefects or #NoEstimates #noManipulatingState
is like #noDefects
or #noEstimates
What is Functional Programming?
It is programming... with functions!
• Pure – Referentially Transparent
• First Class and Higher-Order functions
• Partial application & Currying
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)
Why F#?
• Concise
• Convenient
• Correctness
• Concurrency
• Complete
Concise
Convenient
Correctness
Concurrency
Complete
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”.
We are addicted to accidental complexity
We are addicted to accidental complexity
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)
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]
Functional Type Notation
let add1 x = x + 1 int -> int
let add x y = x + y int -> int -> int
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
Basic List Functions
predicate items result
projection items result
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 )
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
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
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
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# ]