This document provides an overview of functional reactive programming (FRP). It begins by discussing programming paradigms like imperative and declarative programming. FRP is then introduced as a programming paradigm that combines functional programming and reactive programming. Functional programming treats computation as mathematical functions while reactive programming involves asynchronous data streams. The document explains core FRP concepts like streams and signals. It also introduces RxSwift, a library that brings FRP to iOS. Finally, examples are provided to demonstrate the advantages of using an FRP approach.

1. Functional reactive
programming
Hoang Hai Hung
1
September, 2016

2. Outline
1.Programming paradigms
2. Functional reactive programming
3. RxSwift
4. Demo
2

3. What is Programming language ?
A programming language is a notation for writing programs, which are
specifications of a computation or algorithm.
3

4. Programming paradigms
Pascal, C Java, C++ Haskell, Lisp Prolog
Swift 4

5. Imperative vs Declarative
Telling the “machine” how to do
something, and as a result what
you want to happen will happen.
Imperative programming
Telling the “machine” what you
would like to happen, and let the
computer figure out how to do it.
Declarative programming
BUT,
HOW ?
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6. 6
Imperative vs Declarative
Imperative programming Declarative programming
let numbers = [1, 2, 3, 4, 5, 6]
let sum = reduce(numbers, 0, +)
let odds = filter(numbers, { $0 % 2 == 1})
let array = [1, 2, 3, 4, 5, 6]
var sum = 0
var odds = []
for element in array {
sum += element
if element % 2 == 1 {
odds
.append(element)
}
}

7. Imperative vs Declarative
7
Imperative programming Declarative programming

8. Imperative vs Declarative
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9. Imperative way
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10. Imperative way (cont.)
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11. Imperative way (cont.)
Pyramid of Doom
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12. Declarative way
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13. Imperative vs Declarative
Stand up, walk 10 steps by your foot to the
fridge, use your hand to open the door, get
me the water, walk back 10 steps ...
Imperative programming
Honey, i wish i had a glass of cold
water now.
Declarative programming
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Thanks, honeyYou don’t say ?

14. Advantages of Declarative Programming
Minimizes mutability
Reduces state side-effects
More understandable code
More scalable
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15. Outline
1. Programming paradigm
2. Functional reactive programming
3. RxSwift
4. Demo
15

16. Functional reactive programming (FRP)
Functional reactive programming (FRP) is a programming paradigm for
reactive programming using the building blocks of functional programming
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17. Functional programming
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Functional programming is a programming paradigm that treats computation
as the evaluation of mathematical functions and avoids changing-state and
mutable data

18. Functional programming
18
let numbers = [1, 2, 3, 4, 5, 6]
let doubled = numbers.map($0 * $0)
let sum = doubled.reduce(0, combine: +))

19. Reactive programming
Reactive programming is programming with asynchronous data streams.
19

20. Reactive programming
C = A + B
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21. Functional reactive programming
Closure/Lambdas
Pure Function
First-Class Functions
High-Order Functions
Functional
Events/Data – Driven
Push
Asynchronous
Reactive
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https://medium.com/@jugoncalves/functional-programming-should-be-your-1-priority-for-2015-47dd4641d6b9
https://medium.com/reactive-programming/what-is-reactive-programming-bc9fa7f4a7fc

22. Outline
1. Programming paradigm
2. Functional reactive programming
3. RxSwift
4. Demo
22

23. Stream
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A stream is a sequence of ongoing events ordered in time.

24. Stream
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25. Signal
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Signal is a value that changes over time.

26. Example
Khi người dùng thực hiện đồng thời `di chuyển` (pan) và `xoay` vật thể
(rotate), thực hiện đếm ngược từ `3`. Dừng đếm ngược khi người dùng bỏ tay
ra hoặc đếm ngược đến 0.
26

27. Imperative way
27https://gist.github.com/dangthaison91/ab28bf2056f6c8a7240d073d0fb1f563#file-gesture-swift

28. Declarative way (FRP)
28https://gist.github.com/dangthaison91/8dc2ae412a675af322a376884f3f896e#file-gesture_frp-swift

29. Declarative way (FRP)
29

30. 30

31. 31

32. Example
Search on GitHub
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33. Imperative way
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34. Declarative way (FRP)
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35. Advantages of FRP
Code more concise & clear, easy to understand without context
Readability, highly express
Make Asynchronous easier
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36. 36
Conclusion

37. 37
Conclusion

38. 38

39. Outline
1. Programming paradigm
2. Functional reactive programming
3. RxSwift
4. Demo
39

40. THANK YOU !
40