Are you a C# developer who has embraced the language’s functional concepts such as lambda expressions and LINQ, but have not yet embraced F#? In this talk I’ll compare and contrast code written in both C# and F# that will highlight the differences between the two languages while also showing how a functional-first language like F# can be a great tool for solving problems.

1. F#
for the
C# developer
Nate Peterson
@njpetersonpa

2. Brief intro to F#
Thinking functionally
Look at some code

3. Simple vs. Complex
and
Familiar vs. Unfamiliar

4. What’s
NOT
in this talk

5. What is F#?

6. Functional-first language

7. Strongly typed

8. let add x y =
x + y
add 1 1

9. F# is more than just a new language
It’s a new way of thinking

10. Immutability

11. Side-effect free functions

12. Functions are first class

13. let add x y =
x + y
let add42 x =
add 42 x
add42 1

14. let add x y =
x + y
let add42 =
add 42
add42 1

15. Sum of Squares- C#

16. public static class SumOfSquaresHelper
{
public static int Square(int i)
{
return i * i;
}
public static int SumOfSquares(int n)
{
int sum = 0;
for (int i = 1; i <= n; i++)
{
sum += Square(i);
}
return sum;
}
}

17. Sum of Squares- C# (again)

18. public static class FunctionalSumOfSquaresHelper
{
public static int SumOfSquares(int n)
{
return Enumerable.Range(1, n)
.Select(i => i * i)
.Sum();
}
}

19. Sum of Squares- F#

20. let square x = x * x
let sumOfSquares n =
[1..n] |>
List.map square|>
List.sum
sumOfSquares 100

21. Think about…
Concise – no noise
Simple vs. Complex
Familiar vs. Unfamiliar
where are the types
where’s the {}

22. Sum of Squares (evens only)

23. public static class SumOfSquaresHelper
{
public static int Square(int i)
{
return i * i;
}
public static int SumOfSquares(int n)
{
int sum = 0;
for (int i = 1; i <= n; i++)
{
if (i % 2 == 0)
{
sum += Square(i);
}
}
return sum;
}
}

24. public static class FunctionalSumOfSquaresHelper
{
public static int SumOfSquares(int n)
{
return Enumerable.Range(1, n)
.Select(i => i * i)
.Where(i => i % 2 == 0)
.Sum();
}
}

25. let square x = x * x
let isEven x = x % 2 = 0
let sumOfSquares n =
[1..n] |>
List.filter
List.map square|>
List.filter isEven |>
List.sum
sumOfSquares 100

26. FizzBuzz - C#

27. public List<string> Create()
{
var results = new List<string>();
for (var i = 0; i < 100; i++)
{
results.Add(FizzBuzz(i));
}
return results;
}
private static string FizzBuzz(int num)
{
if (num % 3 == 0 && num % 5 == 0)
{
return "FizzBuzz";
}
if (num % 3 == 0)
{
return "Fizz";
}
if (num % 5 == 0)
{
return "Buzz";
}
return num.ToString();
}

28. FizzBuzz - C# (again)

29. public List<string> Create(IEnumerable<int> sequence)
{
return Enumerable.Range(1, 100).Select(FizzBuzz).ToList();
}
private static string FizzBuzz(int num)
{
if (num % 3 == 0 && num % 5 == 0)
{
return "FizzBuzz";
}
if (num % 3 == 0)
{
return "Fizz";
}
if (num % 5 == 0)
{
return "Buzz";
}
return num.ToString();
}

30. FizzBuzz - F#

31. let FizzBuzz number =
match number % 3, number % 5 with
| 0, 0 -> "FizzBuzz"
| 0, _ -> "Fizz"
| _, 0 -> "Buzz"
| _ -> string number
[1..100]
|> List.map FizzBuzz
|> List.reduce (sprintf "%srn%s")

32. Think about…
Concise – again
Pattern matching for flow control

33. Immutable Person – C#

34. public class Person
{
public Person(string firstName, string lastName)
{
}
}

35. public class Person
{
private string _firstName;
private string _lastName;
public Person(string firstName, string lastName)
{
_firstName = firstName;
_lastName = lastName;
}
}

36. public class Person
{
private string _firstName;
private string _lastName;
public Person(string firstName, string lastName)
{
_firstName = firstName;
_lastName = lastName;
}
public string FirstName
{
get
{
return _firstName;
}
}
}

37. public class Person
{
private string _firstName;
private string _lastName;
public Person(string firstName, string lastName)
{
_firstName = firstName;
_lastName = lastName;
}
public string FirstName
{
get
{
return _firstName;
}
}
public string LastName
{
get
{
return _lastName;
}
}
}

38. public class Person
{
private readonly string _firstName;
private readonly string _lastName;
public Person(string firstName, string lastName)
{
_firstName = firstName;
_lastName = lastName;
}
public string FirstName
{
get
{
return _firstName;
}
}
public string LastName
{
get
{
return _lastName;
}
}
}

39. Immutable Person – F#

40. type Person = {FirstName:string; LastName:string}
let nate = {FirstName=“Nate"; LastName=“Peterson"}

41. Nate Peterson
@njpetersonpa