Functional reactive programming (FRP) is a declarative programming paradigm that models reactive systems as streams of values over time. FRP is declarative - code describes what should happen rather than how to make it happen. This makes code more concise and easier to understand. FRP also makes asynchronous code and concurrency easier by eliminating state from code. Thinking reactively can feel complex initially but leads to simpler solutions compared to imperative programming. FRP is a useful programming paradigm worth learning.

1. Reactive Thinking
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2. Functional
Reactive
Programming

3. 1. What is FRP?

4. Functional
+
Reactive

5. Microsoft Excel

6. a = b + c

7. FRP: Streams of values
over time

10. Observable

11. Observable Event
• Next
• Error
• Completed

12. FRP
is
Declarative

13. Imperative
Write correct sequence of codes in the correct
order. Step by step. (HOW)
Declarative
Write code to describes WHAT you want to do.

14. 2. Why is FRP?

15. Example 1
Search API as you type but:
- Don't spam API server every seconds
- Only make request if keyword changed
- Cancel previous requests

16. Imperative

17. Declarative

18. Declarative

20. Declarative

21. Declarative

24. Imperative

25. Declarative

26. Example 2
When the user starts simultaneously panning and
rotating an object, start a countdown from 3.
Stop the timer either when the countdown ends
or when the user stops the gestures.

27. Imperative

28. Imperative

29. Imperative
- When the user touches the screen
- Check if a user is panning an object, store that information
- Check if both gestures are running simultaneously
- Start a timer, from 3, counting down.
- Check if the user is rotating an object, store that information
- Check if both gestures are running simultaneously
- Start a timer, from 3, counting down.
- Check if the user stopped panning
- Stop the timer if needed
- Check if the user stopped rotating
- Stop the timer if needed
- When the timer ticks, decrease the number of seconds left
- If the number of seconds left is zero, stop the timer*

30. There is a Better
Way!

31. Declarative

32. Declarative

33. Declarative

34. Declarative

37. Declarative

38. Declarative

39. Declarative

40. Declarative
Define condition “simultaneously `panning` and `rotating`”
Define condition “start a countdown from `3`”
Define condition “when the user stops the gestures”
Define what a timer is
When the user starts simultaneously `panning` and `rotating` an object, start a countdown from `3`.
Stop the timer either when the countdown ends or when the user stops the gestures.”

41. Advantages
• Code more concise, easy to read, easy to understand
without context
• Make asynchronous easier
• Concurrency, thread safety
• Eliminate state from your code
• Has standard mechanism for error recovery
• Support Data Binding
• Maintainability, Extensibility, Testability
...

42. Denial
• FRP is hard, imperative is more easy
• FRP just is trend!
• RxSwift is just another TOOL
• Unnecessarily complex

44. 3. Thinking in Reactive

45. FRP is hard, but it is
SIMPLE

46. Imperative is EASY

47. Simple
vs
Easy

48. Complexity

49. Simple made Easy
— Rick Hickey

50. FRP is good Trend

51. Functional Reactive
is
RADIOACTIVE

52. More: https://goo.gl/lfNWlJ
Blog: https://dangthaison91.wordpress.com

53. Thank you!