Functional Reactive Programming

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

9. Core of FRP is Signal

10. Signal emits
value over the
time

11. FRP
is
Declarative

12. Imperative
Write correct sequence of codes in the correct
order. Step by step. (How)
Declarative
Write code to describes what you want to do.

13. 2. Why is FRP?

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

15. Imperative

16. Declarative

20. 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.

21. Imperative

22. Imperative

23. 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*

24. There is a Better
Way!

25. Declarative

26. Declarative

27. Declarative

30. Declarative

31. Declarative

32. 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.”

33. Advantages
• Code more concise & clear, easy to
understand without context
• Readability, highly express
• Make Asynchronous easier
• UI Binding
• Maintainability, Extensibility
...

34. Imperative

35. Declarative

36. What we can do
• Observables
• Transformations
• Composition
• Combination
• Filter
• Buffer
...

38. Denial
• FRP is hard, imperative is more easier
• FRP just is trend!
• Just another Framework
• Unnecessarily complex

40. 3. Thinking in Reactive

41. FRP is hard, but it is
SIMPLE

42. Imperative is EASY

43. Simple
vs
Easy

44. Complexity

45. Simple made Easy
— Rick Hickey

46. FRP is good Trend

47. Functional Reactive
will be
RADIOACTIVE

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

49. Thank you!