F# Eye 4 the C# Guy - DDD Cambridge Nights 2014

Phil Trelford, @ptrelford DDD Cambridge Nights, 2014

 Statically Typed  Functional First  Object Orientated  Open Source  .Net language  In Visual Studio & Xamarin Studio

Kaggle The fact that F# targets the CLR was also critical we have a large existing code base in C#, getting started with F# was an easy decision.

The F# code is consistently shorter, easier to read, easier to refactor and contains far fewer bugs. …we’ve become more productive.

Phil Trelford, @ptrelford DDD Cambridge, 2014

F# C# type Person(name:string,age:int) = /// Full name member person.Name = name /// Age in years member person.Age = age public class Person { public Person(string name, int age) { _name = name; _age = age; } private readonly string _name; private readonly int _age; /// <summary> /// Full name /// </summary> public string Name { get { return _name; } } /// <summary> /// Age in years

F# type VerySimpleStockTrader (analysisService:IStockAnalysisService, brokerageService:IOnlineBrokerageService) = member this.ExecuteTrades() = C# public class VerySimpleStockTrader { private readonly IStockAnalysisService analysisService; private readonly IOnlineBrokerageService brokerageService; public VerySimpleStockTrader( IStockAnalysisService analysisService, IOnlineBrokerageService brokerageService) { this.analysisService = analysisService; this.brokerageService = brokerageService; } () // ... public void ExecuteTrades() { // ... } }

F# NUnit C# NUnit module MathTest = using NUnit.Framework; open NUnit.Framework [TestFixture] public class MathTest { [Test] public void TwoPlusTwoShouldEqualFour() { Assert.AreEqual(2 + 2, 4); } } let [<Test>] ``2 + 2 should equal 4``() = Assert.AreEqual(2 + 2, 4)

F# Foq C# Moq let ``order sends mail if unfilled``() = // setup data let order = Order("TALISKER", 51) let mailer = mock() order.SetMailer(mailer) // exercise order.Fill(mock()) // verify verify <@ mailer.Send(any()) @> once public void OrderSendsMailIfUnfilled() { // setup data var order = new Order("TALISKER", 51); var mailer = new Mock<MailService>(); order.SetMailer(mailer.Object); // exercise order.Fill(Mock.Of<Warehouse>()); // verify mailer.Verify(mock => mock.Send(It.IsAny<string>()), Times.Once()); }

type formula = | Neg of formula | Exp of formula * formula | ArithmeticOp of formula * arithmetic * formula | LogicalOp of formula * logical * formula | Num of UnitValue | Ref of int * int | Range of int * int * int * int | Fun of string * formula list

open FSharp.Data type Simple = JsonProvider<""" { "name":"John", "age":94 } """> let simple = Simple.Parse(""" { "name":"Tomas", "age":4 } """) Simple.Age

Phil Trelford, @ptrelford DDD Cambridge, 2014

software stacks trainings teaching F# user groups mac and linux snippets cross-platform books and tutorials F# Software Foundation F# community open-source MonoDevelop http://www.fsharp.org contributions research support consultancy mailing list

//--------------------------------------------------------------// About Let // // The let keyword is one of the most fundamental parts of F#. // You'll use it in almost every line of F# code you write, so // let's get to know it well! (no pun intended) //--------------------------------------------------------------[<Koan(Sort = 2)>] module ``about let`` = [<Koan>] let LetBindsANameToAValue() = let x = 50 AssertEquality x __

Phil Trelford, @ptrelford DDD Cambridge, 2014