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Get Functional on the CLR: Intro to Functional Programming with F#

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

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Get Functional on the CLR: Intro to Functional Programming with F#

  1. 1. Get Functional on the CLR: Intro to Functional Programming with F# David Alpert | @davidalpert | http://about.me/davidalpert
  2. 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. 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. 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. 5. We are addicted to complexity We are addicted to complexity
  6. 6. We are addicted to accidental complexity We are addicted to accidental complexity
  7. 7. We are addicted to manipulating state We are addicted to manipulating state
  8. 8. #noManipulatingState is like #noDefects or #NoEstimates #noManipulatingState is like #noDefects or #noEstimates
  9. 9. What is Functional Programming? It is programming... with functions! • Pure – Referentially Transparent • First Class and Higher-Order functions • Partial application & Currying
  10. 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. 11. Why F#? • Concise • Convenient • Correctness • Concurrency • Complete Concise Convenient Correctness Concurrency Complete
  12. 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. 13. We are addicted to accidental complexity We are addicted to accidental complexity
  14. 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. 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. 16. Functional Type Notation let add1 x = x + 1 int -> int let add x y = x + y int -> int -> int
  17. 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. 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. 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. 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. 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. 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# ]

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