Abstract for the presentation: F# is a language I am passionate about and a language I would like to use on my day job, and for that to be a reality I need you to join me! I want you to join me in the welcoming F# community where you can see a new world open up for you and enabling you to solve problems more efficiently than you do today with C#. F# is not a language that is used only in academia, it is a general purpose language that is growing every day with an awesome community of brilliant people. F# also defines the future of C# in many ways, so if you want to be ahead of the game you should jump on the F# bandwagon today. There are many reasons to learn F# like; a new paradigm will make you a better overall developer, F# will make you write less bugs and you will have more fun at work! I this presentation I will show you: What the strengths of F# are Why you should start using F# How you get started with F# Don't hesitate, join the F# movement. The only way to improve is to change!

1. F# AS OUR DAY JOB BY 2016
Oslo/NDC Oslo
Tomas Jansson
19/06/2015

2. THIS IS ME!
Tomas Jansson
Manager & Practice Lead .NET
BEKK Oslo
@TomasJansson
tomas.jansson@bekk.no
github.com/mastoj
slideshare.net/mastoj
blog.tomasjansson.com

3. http://www.eatsleepcoderepeat.de/beitraege_2013_10.htm

4. Sad &
misunderstood

5. C#
95%
F#
5%
Programming at work in 2015

6. I want to be
the hero!

7. C#
50%
F#
50%
Programming at work in 2016

8. Why change?

9. Time
Awesomeness
TOMAS’ GRAPH OF AWESOMENESS
No change

10. Time
Awesomeness
TOMAS’ GRAPH OF AWESOMENESS
No change
Change

11. Time
Awesomeness
TOMAS’ GRAPH OF AWESOMENESS
No change
Change
You can’t
improve without
change!

12. Application

13. With plumbing
Application

14. Extra complexity
Application

15. Application
Extra complexity

16. Why do I
like F#?
The facts!
What can
you do?

17. Why do I
like F#?

18. #1: Good habits

19. #2: Separation

20. #2: Separation
"Objects are not data structures. Objects may use data structures; but
the manner in which those data structures are used or contained is
hidden. This is why data fields are private. From the outside looking in
you cannot see any state. All you can see are functions. Therefore
Objects are about functions not about state."
Uncle Bob - http://blog.cleancoder.com/uncle-bob/2014/11/24/FPvsOO.html

21. #2: Separation
"Objects are not data structures. Objects may use data structures; but
the manner in which those data structures are used or contained is
hidden. This is why data fields are private. From the outside looking in
you cannot see any state. All you can see are functions. Therefore
Objects are about functions not about state."
Uncle Bob - http://blog.cleancoder.com/uncle-bob/2014/11/24/FPvsOO.html

22. #3: Null handling

23. #3: Null handling
Null References: The Billion Dollar Mistake
- Sir Charles Antony Richard Hoare
http://tinyurl.com/TheBillionDollarMistake

24. #3: Null handling
type Order = {OrderId: int; Total: int}
let getOrder orderId =
match orderId with
| 0 -> None
| _ -> Some { OrderId = orderId
Total = 23*orderId }
let printOrder order =
match order with
| Some o ->
printfn "Order id: %i, Total: %i«
o.OrderId o.Total
| None ->
printfn "No order"

25. #3: Null handling
type Order = {OrderId: int; Total: int}
let getOrder orderId =
match orderId with
| 0 -> None
| _ -> Some { OrderId = orderId
Total = 23*orderId }
let printOrder order =
match order with
| Some o ->
printfn "Order id: %i, Total: %i«
o.OrderId o.Total
| None ->
printfn "No order"
Returns
Order option

26. #3: Null handling
type Order = {OrderId: int; Total: int}
let getOrder orderId =
match orderId with
| 0 -> None
| _ -> Some { OrderId = orderId
Total = 23*orderId }
let printOrder order =
match order with
| Some o ->
printfn "Order id: %i, Total: %i«
o.OrderId o.Total
| None ->
printfn "No order"
Returns
Order option
Explicit null
handling!

27. #3: Null handling
public class Order
{
public int OrderId { get; set; }
public int Total { get; set; }
}
public Order GetOrder(int orderId)
{
if (orderId == 0) return null;
return new Order() {
OrderId = orderId,
Total = 23*orderId };
}
public void PrintOrder(Order order)
{
Console.WriteLine("Order id: {0}, Total: {1}",
order.OrderId, order.Total);
}

28. #3: Null handling
public class Order
{
public int OrderId { get; set; }
public int Total { get; set; }
}
public Order GetOrder(int orderId)
{
if (orderId == 0) return null;
return new Order() {
OrderId = orderId,
Total = 23*orderId };
}
public void PrintOrder(Order order)
{
Console.WriteLine("Order id: {0}, Total: {1}",
order.OrderId, order.Total);
}
How do I
differ success
from failure?

29. #3: Null handling
public class Order
{
public int OrderId { get; set; }
public int Total { get; set; }
}
public Order GetOrder(int orderId)
{
if (orderId == 0) return null;
return new Order() {
OrderId = orderId,
Total = 23*orderId };
}
public void PrintOrder(Order order)
{
Console.WriteLine("Order id: {0}, Total: {1}",
order.OrderId, order.Total);
}
How do I
differ success
from failure?
What about
null?

30. #4: Types

31. #4: Types
type Customer =
{ CustomerId: Guid
FirstName: string
LastName: string }

32. #4: Types
public class Customer
{
public Guid CustomerId { get; private set; }
public string FirstName { get; private set; }
public string LastName { get; private set; }
public Customer(Guid customerId, string firstName, string lastName)
{
CustomerId = customerId;
FirstName = firstName;
LastName = lastName;
}
protected bool Equals(Customer other)
{
return CustomerId.Equals(other.CustomerId) &&
string.Equals(FirstName, other.FirstName) &&
string.Equals(LastName, other.LastName);
}
public override bool Equals(object obj)
{
if (ReferenceEquals(null, obj)) return false;
if (ReferenceEquals(this, obj)) return true;
if (obj.GetType() != this.GetType()) return false;
return Equals((Customer) obj);
}
public override int GetHashCode()
{
unchecked
{
var hashCode = CustomerId.GetHashCode();
hashCode = (hashCode*397) ^ (FirstName != null ? FirstName.GetHashCode() : 0);
hashCode = (hashCode*397) ^ (LastName != null ? LastName.GetHashCode() : 0);
return hashCode;
}
}
}

33. #5: Type providers
Strongly typed «ORM»
SQL JSON XML WCF …

34. #5: Type providers

35. #6: Readability

36. #6: Readability

37. #6: Readability

38. #6: Readability

39. #6: Readability

40. #6: Readability

41. #6: Readability

42. #6: Readability

43. #6: Readability

44. #6: Readability

45. #6: Readability

46. #6: Readability

47. #6: Readability

48. #6: Readability

49. #6: Readability

50. #6: Readability

51. #6: Readability
// Version 1
let executeCommand command =
command |> validate |> log |> execute |> log
let result = executeCommand command
// Version 2
let executeCommand = validate >> log >> execute >> log
let result = executeCommand command

52. #6: Readability
// Version 1
public ExecutionResult ExecuteCommand(Command command)
{
return Log(Execute(Log(Validate(command))));
}
var result = ExecuteCommand(new Command());
// Version 2
public ExecutionResult ExecuteCommand(Command command)
{
var validationResult = Validate(command);
Log(validationResult);
var executionResult = Execute(validationResult);
Log(executionResult);
return executionResult;
}
var result = ExecuteCommand(new Command());

53. The facts!

54. @simontcousins
@ScottWlaschin
http://tinyurl.com/CyclesInTheWild
http://tinyurl.com/DoesTheLanguageMakeADifference

55. Cycles
Compared 10 C# projects with 10 F# projects
Compared «top-level» types
Top-level type: “a type that is not nested and
which is not compiler generated”
@ScottWlaschin
http://tinyurl.com/CyclesInTheWild

56. PROJECTS
Mono.Cecil, which inspects programs and libraries in the
ECMA CIL format
NUnit
SignalR for real-time web functionality
NancyFx, a web framework
YamlDotNet, for parsing and emitting YAML
SpecFlow, a BDD tool
Json.NET
Entity Framework
ELMAH, a logging framework for ASP.NET
NuGet itself
Moq, a mocking framework
NDepend, a code analysis tool
FSharp.Core, the core F# library.
FSPowerPack.
FsUnit, extensions for NUnit.
Canopy, a wrapper around the Selenium test automation
tool.
FsSql, a nice little ADO.NET wrapper.
WebSharper, the web framework.
TickSpec, a BDD tool.
FSharpx, an F# library.
FParsec, a parser library.
FsYaml, a YAML library built on FParsec.
Storm, a tool for testing web services.
Foq, a mocking framework.
C# F#

61. SpecFlow

62. SpecFlow
I do think SpecFlow is great tool!

63. TickSpec

64. Does your
language
matter?
Application to assist in maintaining the stability and security
of the electricity supply in the UK
Existing solution almost fully implemented in C#
Rewritten in F#
@simontcousins
http://tinyurl.com/DoesTheLanguageMakeADifference

67. “The C# project took five years and peaked at ~8 devs. It never fully
implemented all of the contracts.
The F# project took less than a year and peaked at three devs (only one had
prior experience with F#). All of the contracts were fully implemented.”
http://tinyurl.com/DoesTheLanguageMakeADifference

68. THE LANGUAGE YOU USE MAKE A DIFFERENCE
Encapsulated small types
Less top-level dependencies
Less «leaky» abstractions
Types and functions must be
defined
Prevents cycles
Encapsulation
Much easier to do in F#
Linear Generics

69. What can
you do?

70. ReadCode

72. http://fsharp.org/
http://www.meetup.com/OsloFSharp/
https://twitter.com/hashtag/fsharp

73. http://www.peoplevine.com/page/peoplevine-for-startups
Start small,
but think big!

74. Demo?

75. RESOURCES
http://fsharpforfunandprofit.com/
http://tinyurl.com/DoesTheLanguageMakeADifference
http://www.meetup.com/OsloFSharp/ (if you live in Oslo)
http://fsharp.org/

76. Questions?

77. Thank you!
@TomasJanssonVote!