1. FP in Scala
Enero 2015

2. WHY FP?
• FP Concepts
• FP “powers”
1 2 3FP IN SCALA: THE BASICS
• Mutability vs
Immutability
• HOFs
• Functions = First-class
citizens
FP TOOLS
• For-comprehension
(desugaring)
• Try & Either
ÍNDICE

3. WHY FP?
1

4. Functional Programming in Scala
1.1 FP Concepts: Pure Function
A function of type A => B maps
every value of type A to exactly
one value of type B
And does nothing else
“Nothing else” = Side effects: Modifying a data structure,
setting a field on a object, throwing an exception,
printing to the console, reading from or writing to a file
1 WHY FP?

5. Functional Programming in Scala
1.1 FP Concepts: Referential transparency
1 WHY FP?
If you have an expression, this expression is RT if you can evaluate
it and then replace this expression with the value that you get
A function is pure if f(x) is RT when x is RT

6. Functional Programming in Scala
1.1 FP Concepts: Scala is not a purely functional language!!
1 WHY FP?

7. Functional Programming in Scala
1.2 FP “Powers”: Testability
1 WHY FP?

8. Functional Programming in Scala
1.2 FP “Powers”: Testability
1 WHY FP?

9. Functional Programming in Scala
1.2 FP “Powers”: Testability
1 WHY FP?

10. Functional Programming in Scala
1.2 FP “Powers”: Testability
1 WHY FP?

11. Functional Programming in Scala
1.2 FP “Powers”: Reusability
1 WHY FP?

12. Functional Programming in Scala
1.2 FP “Powers”: Reusability
1 WHY FP?

13. Functional Programming in Scala
1.2 FP “Powers”: Reusability
1 WHY FP?

14. Functional Programming in Scala
1.2 FP “Powers”: Reusability
1 WHY FP?

15. Functional Programming in Scala
1.2 FP “Powers”: Reusability
1 WHY FP?

16. Functional Programming in Scala
1.2 FP “Powers”: Parallelizability
1 WHY FP?

17. Functional Programming in Scala
1.2 FP “Powers”: Comprehension
1 WHY FP?

18. FP IN SCALA:
THE BASICS2

19. Functional Programming in Scala
2.1 Mutability vs Immutability
2 FP IN SCALA: THE BASICS

20. Functional Programming in Scala
2.1 Mutability vs Immutability
2 FP IN SCALA: THE BASICS

21. Functional Programming in Scala
2.1 Mutability vs Immutability
2 FP IN SCALA: THE BASICS

22. Functional Programming in Scala
2.1 Mutability vs Immutability
2 FP IN SCALA: THE BASICS
All the classes that mix-in this trait should be in this file
A is covariant

23. Functional Programming in Scala
2.1 Mutability vs Immutability
2 FP IN SCALA: THE BASICS
Variadic function syntax
Tail call annotation

24. Functional Programming in Scala
2.2 Higher Order Functions
2 FP IN SCALA: THE BASICS

25. Functional Programming in Scala
2.3 Functions = First-class citizens
2 FP IN SCALA: THE BASICS
Method
Function

26. Functional Programming in Scala
2.3 Functions = First-class citizens
2 FP IN SCALA: THE BASICS
Function literal
Function value

27. FP TOOLS
3

28. Functional Programming in Scala
3.1 For-comprehension
3 FP TOOLS

29. Functional Programming in Scala
3.1 For-comprehension
3 FP TOOLS

30. Functional Programming in Scala
3.1 For-comprehension
3 FP TOOLS

31. Functional Programming in Scala
3.1 For-comprehension
3 FP TOOLS

32. Functional Programming in Scala
3.1 For-comprehension
3 FP TOOLS

33. Functional Programming in Scala
3.1 For-comprehension
3 FP TOOLS

34. Functional Programming in Scala
3.1 For-comprehension
3 FP TOOLS
flatMap

35. Functional Programming in Scala
3.1 For-comprehension
3 FP TOOLS
http://docs.scala-lang.org/tutorials/FAQ/yield.html

36. Functional Programming in Scala
3.1 For-comprehension
3 FP TOOLS

37. Functional Programming in Scala
3.1 For-comprehension
3 FP TOOLS

38. Functional Programming in Scala
3.1 For-comprehension
3 FP TOOLS

39. Functional Programming in Scala
3.1 For-comprehension
3 FP TOOLS

40. Functional Programming in Scala
3.1 For-comprehension
3 FP TOOLS
What else??
Monads!!!
Future
Try
Iteratee
RDD
(warning!)
...

41. Functional Programming in Scala
3.2 Try & Either
3 FP TOOLS
Alternatives to “pure” exceptions
Why?
1º. Exceptions break RT
2º. Exceptions are NOT type-safe

42. Functional Programming in Scala
3.2 Try & Either
3 FP TOOLS

43. Functional Programming in Scala
3.2 Try & Either
3 FP TOOLS
//Awesome Dataviiiiiis code ;)

44. Functional Programming in Scala
3.2 Try & Either
3 FP TOOLS
//Awesome Dataviiiiiis code ;)

45. Functional Programming in Scala
3.2 Try & Either
3 FP TOOLS

46. Functional Programming in Scala

47. Functional Programming in Scala
Functional way “powers” =>
Testability, Reusability, Parallelizability,
Comprehension
Immutability & HOFs
For-comprehension => map, flatMap, filter
Functional way => Handling exceptions