This document discusses functional reactive programming (FRP). It defines FRP as a programming paradigm oriented around data flows and propagation of change. Reactive programming describes systems that are responsive, resilient, elastic and message-driven. The document introduces reactive extensions (Rx) as a library for composing asynchronous and event-based programs using observable sequences and LINQ-style query operators. It provides examples of how Rx can be used to map, filter, scan and zip observable sequences.

1. DEV07
Functional Reactive Programming
Alessandro Melchiori
alessandro@codiceplastico.com - @amelchiori
http://melkio.codiceplastico.com/

2. Grazie a
Platinum
Sponsor

3. Functional Reactive Programming

4. Functional Reactive Programming

5. It's declarative, stateless, side-effects free and immutable
Functional programming

6. It's declarative, stateless, side-effects free and immutable
Functional programming
describes what we
want, not how we want
it

7. It's declarative, stateless, side-effects free and immutable
Functional programming
describes what we
want, not how we want
it
system relys only on
inputs, not external
state

8. It's declarative, stateless, side-effects free and immutable
Functional programming
describes what we
want, not how we want
it
system relys only on
inputs, not external
state
once value has been set,
we can't override its
value
Return new value,
instead of altering
existing ones

9. Give me five functions
and I’ll raise up the world
[map; filter; reduce; collect; zip]

10. let source = [ 1; 2; 3]
let result =
List.map (fun x -> x*2) source
val result : int list = [2; 4; 6]
map

11. let source = [ 1; 2; 3]
let result =
List.filter (fun x -> x > 1) source
val result : int list = [2; 3]
filter

12. let source = [ 1; 2; 3]
let result =
List.reduce (fun acc curr -> acc + curr) source
val result : int = 6
reduce

13. let source = [ [ 1; 2; 3]; [ 4; 5 ] ]
let result =
List.collect (fun x -> x) source
val result : int list = [1; 2; 3; 4; 5; 6]
collect

14. let source1 = [ 1; 2; 3]
let source2 = [‘A’;’B’;’C’]
let result =
List.zip source1 source2
val res : (int * char) list = [(1, 'A'); (2, 'B'); (3, 'C')]
zip

15. Functional Reactive Programming

16. Functional Reactive Programming

17. A programming paradigm oriented around data flows
and the propagation of change.
Reactive programming

18. Reactive systems are responsive, resilient, elastic and message driven
Reactive manifesto (http://www.reactivemanifesto.org/)
Reactive programming

19. Reactive programming
1
2
sum
1diff
4
…readily responsive to a stimulus…

20. Reactive programming
1
1
sum
1diff
4

21. Reactive programming
1
1
sum
1diff
4

22. Reactive programming
1
1
sum
1diff
4

23. Reactive programming
1
1
sum
1diff
4

24. Reactive programming
1
1
sum
1diff
4

25. Reactive programming
1
1
sum
1diff
4

26. Reactive programming
1
1
sum
2diff
4

27. Reactive extensions

28. Rx is a library for composing asynchronous and event-based programs
using observable sequences and LINQ-style query operators
(https://msdn.microsoft.com/en-us/data/gg577609.aspx)
Reactive extensions

29. Rx is a library for composing asynchronous and event-based programs
using observable sequences and LINQ-style query operators
(https://msdn.microsoft.com/en-us/data/gg577609.aspx)
Reactive extensions

30. Rx is a library for composing asynchronous and event-based programs
using observable sequences and LINQ-style query operators
(https://msdn.microsoft.com/en-us/data/gg577609.aspx)
Reactive extensions

31. Rx is a library for composing asynchronous and event-based programs
using observable sequences and LINQ-style query operators
(https://msdn.microsoft.com/en-us/data/gg577609.aspx)
Reactive extensions

32. Rx is a library for composing asynchronous and event-based programs
using observable sequences and LINQ-style query operators
(https://msdn.microsoft.com/en-us/data/gg577609.aspx)
Reactive extensions

33. • a set of types representing asynchronous data streams
• a set of operators to query asynchronous data streams
• a set of types to parameterize concurrency
Reactive extensions

34. RX = Observables + LINQ +
Schedulers

35. demo
intro

36. Reactive extensions

37. Reactive extensions
publisher

38. Reactive extensions
publisher subscriber

39. Reactive extensions
publisher subscriberboth

40. The Observable type adds two missing semantics to the Gang of Four's
Observer pattern, which are available in the Iterable type:
• The ability for the producer to signal to the consumer that there is no
more data available
• The ability for the producer to signal to the consumer that an error
has occurred
Reactive extensions

41. Reactive extensions

42. RX mantra
everything can be a stream

43. Reactive extensions: map
1 2 3 4
A B C D

44. Reactive extensions: filter
1 2 3 4
2 4

45. Reactive extensions: scan
1 2 3 4
1 3 6 10

46. Reactive extensions: zip
1 2 3 4
1, A 2, B 3, C 4, D
A B C D

47. demo
Clicks counter

48. Reactive extensions

49. demo
Autocomplete textbox

50. Recap
• Functional programming
• Reactive programming
• Reactive extensions (Rx.*)

51. FRP is agnostic about languages.
It's a mindset

52. Q&A
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