Presented by: Gopal S. Akshintala, Microsoft Presented at All Things Open 2020 Abstract: A Metric-driven approach to reduce Cognitive Complexity in a code base, using Functional Programming, demoed **hands-on**, by solving a complex real-world ubiquitous design challenge - REST API Bulk Request Validation, with an extensible Framework that separates what-to-do (Validations) from how-to-do (Validation Orchestration). Let's do a case study of a successful implementation done by our team in the world's largest SaaS org, _Salesforce_, through our in-house baked FOSS library **Vader**.

1. overfullstack.github.io

2. FP is cool 😎, coz
it’s complex enough to
make devs feel like
they are doing
something smart!
@GopalAkshintala
- Some Manager (Not Mine!)

3. @GopalAkshintala

4. Dev
Holy
Wars
@GopalAkshintala

5. IDE Theme
Light
Vs
Dark
@GopalAkshintala

6. Eclipse
Vs
Intellij
@GopalAkshintala

7. OOP Vs FP ?
@GopalAkshintala

8. @GopalAkshintala
Immutability
Referential Transparency
Side-effects @ Boundaries
FP Principles
…………………………………………………
…………………………………………………
OOP Principles

9. Imperative
Vs
Declarative
The Jotlin
Dev
@GopalAkshintala

10. Imperative
Code
-
-
-
Imperative
@GopalAkshintala

11. Let’s Concatenate
last names in a
team with a
delimiter 🤝
lastName1 🤝 lastName2 🤝 lastName2
@GopalAkshintala
Team Building!

12. @GopalAkshintala
What about
Corner cases?

13. @GopalAkshintala
lastName1 🤝 lastName2 🤝 lastName2 🤝

14. @GopalAkshintala

15. @GopalAkshintala
Imperative Declarative

16. @GopalAkshintala
Imperative Declarative

17. @GopalAkshintala
Imperative Declarative

18. @GopalAkshintala
Imperative Declarative

19. @GopalAkshintala
Imperative Declarative

20. Declarative
Imperative
Code
-
-
-
Imperative
Vs
Declarative
@GopalAkshintala

21. The Java
@GopalAkshintala

22. But is FP just about
Style?

23. How to Concatenate
Last names in
Parallel?
@GopalAkshintala

24. @GopalAkshintala
How to make this Parallel?

25. How-to-dos What-to-dos
Looping through
the list
Aggregating the
results
Validating the
names
Extracting last
names
@GopalAkshintala

26. @GopalAkshintala
Serial Parallel

27. The
Context:Core
Philosophy
Do
Things differently
without
doing
Different things!
@GopalAkshintala

28. Sequence
Busted
@GopalAkshintala

29. @GopalAkshintala
Reading about
Functors, Monads, Applicatives!

30. Either Monad
EggValidation Failure
Context
@GopalAkshintala
Left Right

31. Source @GopalAkshintala

32. Source @GopalAkshintala

33. Source @GopalAkshintala
Left State
Stays Left

34. Source @GopalAkshintala
f(g(h(x)))

35. Are Monads used in
Enterprise
Software?
@GopalAkshintala

36. The
Vader
@GopalAkshintala

37. REST
APIs
@GopalAkshintala

38. REST
Payload
@GopalAkshintala

39. @GopalAkshintala

40. The
Batch
Validation
Framework
@GopalAkshintala

41. @GopalAkshintala

42. Framework
Requirements
@GopalAkshintala

43. @GopalAkshintala
Validation layer
Service layer
DB layer
Aggregated Response

44. Framework
Meta
Requirements
@GopalAkshintala

45. @GopalAkshintala

46. One Egg
One Validation
Many Eggs
One Validation
@GopalAkshintala

47. Many Eggs
Many Validations
!
@GopalAkshintala

48. Chaos
@GopalAkshintala

49. Chain of Responsibility
@GopalAkshintala
Is FP the Best Fit?

50. @GopalAkshintala
2D ProblemEggs
Validations

51. Making of a
Extensible Machine
@GopalAkshintala
Validations Configuration Orchestration
(What-to-do) (How-to-do) (How-to-do)

52. Immutable
Eggs
@GopalAkshintala

53. Heterogeneous
DataTypes in pipeline
@GopalAkshintala

54. Uniform DataTypes
with Monad Boxes
@GopalAkshintala

55. Standardize
Validations
@GopalAkshintala

56. @GopalAkshintala
val validate1Simple: Validator<Egg, ValidationFailure> = {
if (simpleRule(it)) true.right() else NO_EGG_TO_VALIDATE_1.left()
}
validate1Simple
fun validate1(
badEggFailureBucketMap: MutableMap<Int, ValidationFailure>,
eggIndex: Int,
iterator: MutableIterator<Egg?>,
eggToBeValidated: Egg?
): Boolean {
if (!simpleRule(eggToBeValidated)) {
iterator.remove()
badEggFailureBucketMap[eggIndex] = ValidationFailures.NO_EGG_TO_VALIDATE_1
return false
}
return true
}

57. @GopalAkshintala
Validator
typealias Validator<ValidatableT, FailureT>
= suspend (ValidatableT) -> Either<FailureT, Any?>

58. Framework
How-to-dos
@GopalAkshintala

59. @GopalAkshintala
Lift

60. @GopalAkshintala
Lift

61. Framework
How-to-dos
@GopalAkshintala

62. Transformation
map
flatMap
filter
take…
Aggregation
reduce
groupBy
zip,unzip
fold,foldRight
scan,runningReduce
@GopalAkshintala
Dozen FP Operations for
Daily Programming

63. Framework
How-to-dos
@GopalAkshintala

64. What about
Complexity?
@GopalAkshintala

65. FP is NOT Complex
It fights
Cognitive-Complexity
@GopalAkshintala

66. Min.
Cognitive-Complexity
Same
Time-Complexity
@GopalAkshintala

67. Railway-Oriented
Programming
@GopalAkshintala

68. @GopalAkshintala
bit.ly/imp-vs-dec
bit.ly/ro-validation-kt
bit.ly/fcwfp-kt-slides
{ }

69. @GopalAkshintala

70. @GopalAkshintala
gopal.akshintala@gmail.com

71. @GopalAkshintala