An introduction to Functional Programming paradigme

1. Functional
Programming 𝝺
Kamel Ouzouigh

2. Highlights
● Pure Functions
● Functional Features
● ADT
● Pattern Matching
● Exception Handling
● Monads

3. What is Functional Programming ?
Pure functions
Immutable values
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2

4. Pure function
Given the same input, will always return the same output
Doesn’t have any side effects
1
2

5. Pure function
// pure
Math.Max(5, 8)
"Typescript".Length
"Typescript".ToUpper()
var numbers = new List<int> { 0, 8, 9, 1 };
numbers.OrderBy(x => x)
numbers.Where(x => x % 2 == 0)
// impure
var numbers = new List<int> { 0, 8, 9, 1 };
numbers.Sort();
Action<String> greeting = name =>
{
Console.WriteLine("hi" + name + " !");
}

6. Benefits of pure functions
Easier to reason about
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3
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5
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7
Easier to combine
Offer Referential Transparency
Easier to parallelize
Are Memoizable
Can be lazy
Easier to test

7. How about I/O ?
I/O Wrapper code

8. Functional features

9. What is a Function?
Map between values (ex: string -> int)
Methods, Lambdas, Maps
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2

10. Functions are values

11. Full Applied Function

12. Partially Applied Function

13. Currying

14. Currying
Example

15. Pattern Matching

16. Algebraic Data Type(ADT)
Algebra consists of:
A set of objects
The operations that can be applied to those objects to create new objects
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Examples
Numeric Algebra
Relational Algebra

17. Algebraic Data Type(ADT)
Algebraic Data Types are combination of other types

18. Algebraic Data Type(ADT)

19. Algebraic Data Type(ADT)
Product Type

20. Algebraic Data Type(ADT)

21. Algebraic Data Type(ADT)
Sum Type

22. Pattern Matching
A pattern match combines an applicability test and destructuring bind
Destructuring bind extract values from an object
Applicability test determines if the pattern matches the target
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23. Pattern Matching
Over Composition

24. Pattern Matching
Over Inheritance / Closed Hierarchy

25. Pattern Matching
Over Inheritance / Closed Hierarchy

26. Pattern Matching
Over Inheritance / Closed Hierarchy

27. Pattern Matching
Over Inheritance / Closed Hierarchy / C#8

28. Handling Errors

29. Null Exception Problem

30. Alternatives to Null
How to deal with Null value ?

31. FP Solution
SAFETY BOX

32. Null Check FP Solution

33. Null Check FP Solution
Accessing Values

34. Functor

35. Functor
Accessing Values

36. Functor

37. Monad

38. Monad
flatMap aka Bind

39. Monad

40. Monad

41. Option aka Maybe

42. Option aka Maybe

43. Either Type

44. Either Type

45. Either Type

46. Either Type

47. Other Monads
IO
Try
State
Writer
Reader
Seq
Eval
Future