This document discusses functional programming concepts in Kotlin including collections, sequences, and functions. It explains that functional programming uses functions as first-class citizens and avoids shared and mutable state for improved testability and concurrency. Collections and sequences are constructed in different ways, with sequences being lazily evaluated. Common collection operations like map, filter, and reduce are covered along with when to use sequences versus collections.

1. Kotlin
Functional programming basic
Julian

2. Overview
- Functional Programming
- Collection and Sequence

3. Functional programming
● A programming paradigm (like OOP)
● Declarative programming
● Programs are constructed by applying and composing functions
(source: wiki)

4. Declarative
programming
Imperative
programming

5. Concept
● Functions as first-class citizens
● Avoid shared and mutable state
(source:
https://blog-c7ff.kxcdn.com/blog/wp-content/uploa
ds/2016/10/black.png)
Advantage
● No side effect, easy for testing and
concurrency
● Readability and simplicity

6. Functions as first-class citizens
(first-class function)
Ex. Higher-order functions : function as return value or as argument

7. Avoid shared and mutable state
No change, immutable in input

8. FP
● Data
● Math
OOP
● State
● Object to real word

9. Collection and
Sequence

10. Iterator

12. Collections
https://kotlinlang.org/docs/reference/collectio
ns-overview.html

13. Constructing Collections
● listOf<T>
● setOf<T>
● mutableListOf<T>
● mutableSetOf<T>
● mapOf<T>
● mutableMapOf()
Constructing Collections

14. Constructing Sequences
● From elements
● From Iterable
● From function
● From chunks
https://kotlinlang.org/docs/reference/sequenc
es.html#constructing

15. generateSequence
0, 2, 4, 6, 8,10...

16. 1 2 3 4 5 1 2 3 4 5
map{x -> x+3}
take(3)
collection sequence
toList

17. 1 2 3 4 5 1 2 3 4 5
4 5 6 7 map{x -> x+3}
take(3)
collection sequence
toList 4
8

18. 1 2 3 4 5 1 2 3 4 5
4 5 6 7
4 5
map{x -> x+3}
take(3)
collection sequence
toList 4 5
8
6

19. 1 2 3 4 5 1 2 3 4 5
4 5 6 7
4 5
map{x -> x+3}
take(3)
collection sequence
toList 4 5 6
6
8

20. Collection vs Sequence
When to Use Sequences
https://kotlinlang.org/docs/reference/sequenc
es.html#sequence-processing-example

21. Performance
● measureTimeMills example in terminalOperation.kt
● https://gist.github.com/ajalt/c6c120c7cc13a49bc2a8bf62d433d455

22. What will be printed?
Eager vs Lazy loading

23. Eager vs Lazy loading

24. Eager vs Lazy loading
Sequence doesn’t produce result at this moment

25. Sequence: intermediate and terminal operation

26. intermediate and terminal operation
See comments in source code

27. Kotlin Collections and Collection Extension Functions
http://jussi.hallila.com/Kollections/
https://kotlinlang.org/docs/reference/collectio
n-operations.html#common-operations
● Operators
● Transformers
● Aggerations
● Checks and Actions
● Filters

28. Operators
● Plus
● Minus

29. Transformers
● Map
● Sorted / SortedByDescending
● Flatten
● Zip
● Reversed

30. Aggregators
● GroupBy
● Chunked
● Average/Max/Min/Sum
● Reduce/Fold

31. Checks and Actions
● ForEach
● Any/All/ None
● Contains

32. Filters
● Filter
● Take
● First/Last/Single (FirstOrNull…..)
● Distinct

33. Hints: Terminal operation
● ToList
● Sorted

34. Hints: Simplicity

35. Reference
● Code for challenges https://github.com/Julian-Chu/kotlin-collection-sequence
● https://typealias.com/guides/when-to-use-sequences/
● https://kotlinlang.org/docs/reference/collections-overview.html

36. Links
https://winterbe.com/posts/2018/07/23/kotlin-sequence-tutorial/ (by Gx)
https://www.educba.com/functional-programming-vs-oop/ (by Gx)
https://www.guru99.com/functional-programming-tutorial.html (by Gx)
https://medium.com/@przemek.materna/curried-kotlin-48166885ddfa (by Jimin Hsieh)
https://arrow-kt.io/docs/0.10/effects/io/ (by Jimin Hsieh)