RecurSD: Intro to FSharp

Presentation used for the RecurSD (the Functional Programming Conference in San Diego, CA) on January 18th 2014.

Transcript

1. INTRODUCTION TO F# César López-Natarén cesar.nataren at gmail.com
2. WELCOME TO RECURSD 2014 THANKS A LOT TO THE ORGANIZERS & ATTENDEES
3. WHAT IS F#? Functional programming language (that also supports object- oriented and imperative programming) Created by at Microsoft Research Production quality compiler, tools, libraries, and support Full blown project and ecosystem The core of the language was inspired by and code runs in the .NET framework Extended to be a first class language in the Don Syme Open Source OCaml CLI
4. WHAT IS FUNCTIONAL PROGRAMMING? A programming style which utilizes higher order functions and minimizes effects on FP
5. HIGHER ORDER FUNCTIONS IN F# let toThePower xs power = Seq.map power xs let squares = toThePower [1; 2; 3; 4] (fun x -> x * x) let cubes = toThePower [1; 2; 3; 4] (fun x -> x * x * x)
6. HOF IN F# (2) let (|>) x f = f x let toThePower xs power = Seq.map power xs let xs = toThePower [1; 2; 3; 4] let squares = (fun x -> x * x) |> xs let cubes = (fun x -> x * x * x) |> xs
7. HOF IN F# (3) let squaredEvens = [1; 2; 3; 4] |> Seq.filter (fun x -> x % 2 = 0) |> Seq.map (fun x -> x * x) |> Seq.sum
8. MINIMIZING EFFECTS In all of the previous examples, the original data structure was never modified let myList = [1; 2; 3; 4; 5] let newList = myList |> Seq.map (fun x -> x + 2) |> Seq.toList myList newList
9. MINIMIZING EFFECTS (2) type User = { FirstName : string; LastName : string; } let johnDoe = { FirstName = "John"; LastName = "Doe" } let johnSmit = { johnDoe with LastName = "Smith" }
10. MINIMIZING ERRORS Discriminated Unions type Option<'a> = | Some of 'a | None let printKind something = match something with | Some x -> x.GetType().Name
11. MINIMIZING ERRORS (2) type Person(name : string) = member this.Name = name let printName (p : Person) = printfn "%s" p.Name printName (Person "Haskell Curry") printName null
12. SO FAR WE HAVE SEEN Higher order functions enable the creation of abstractions that compose Limiting side effects let us have a simpler mental (and real) execution model for our programs
13. WORKING WITH COLLECTIONS AND COMPUTATIONS IN F# Sequence expressions: Asynchronous expressions:
14. SEQUENCES Unified way to work with collections Based on the interface, abbreviated as in F# Declarative way to express: Collections creation Aggregation Iteration
15. RANGE SEQUENCE EXPRESSIONS seq { 1 .. 10 } seq { -34.0 .. -30.0 } seq { 1.0 .. 3.3 .. 20.0 }
16. SEQ MODULE Aggregator functions Seq.map Seq.toList Seq.toArray ...
17. SEQ EXAMPLE open System.IO let rec allFiles dir = Seq.append (dir |> Directory.GetFiles) (dir |> Directory.GetDirectories |> Seq.map allFiles |> Seq.concat) allFiles "/sbin" |> Seq.map (fun filename -> (filename.Length, filename)) |> Seq.sortBy (fun t -> (fst t)) |> Seq.take(10) |> Seq.toArray
18. ASYNCHRONOUS WORKFLOWS Unified and declarative way to work with asynchronous computations Does not block a thread when I/O happens Sleeps happen Or other async operation is scheduled Based on the Async<'T> type at its core Which represents a value of type 'T at some point in the future Preserves the readability of synchronous code (avoid nested callbacks
19. ASYNC WORKFLOWS open System.Net open Microsoft.FSharp.Control.WebExtensions let tprintfn fmt = printf "[Thread %d]" System.Threading.Thread.CurrentThread.ManagedThreadId; printfn fmt let urlList = [ "Wikipedia", "http://www.wikipedia.org" "The Times", "http://www.nytimes.com" "Le Monde", "http://www.lemonde.fr" ] let fetchAsync(name, url:string) = async { try let uri = new System.Uri(url) let webClient = new WebClient() let! html = webClient.AsyncDownloadString(uri) tprintfn "Read %d characters for %s" html.Length name with | ex -> tprintfn "%s" (ex.Message); } urlList |> Seq.map fetchAsync |> Async.Parallel |> Async.RunSynchronously |> ignore
20. AS YOU MIGHT HAVE NOTICED Sequences and Async workflows (& query expressions, which I didn't show you) have a common "shape" They are generally known as Computation Expressions You can define your own! Create a builder type Implement the special methods that define how the fragments of the computation are combined: Bind Return Zero etc
21. F# MAIN BENEFITS Strong static types without being verbose Type inference Concise syntax Awesome support for functional programming Less typing, more thinking, yields correct code
22. REAL WORLD USAGE web framework distributed computations data and time series manipulation library Prevalent usage in the financial services industry and case studies WebShaper {m}brace Deedle Testimonials
23. SKIPPED TOPICS Type providers Active patterns Code quotations etc
24. RESOURCES @ Twitter Talk " " by Don Syme Fsharp.Org FSharp for fun and profit Visual F# FSharp code snippets #fsharp F# in the open source world Books
25. THANKS!