The document covers topics related to functional programming and ReactiveCocoa including: 1. It discusses the concepts of functional reactive programming where time is an implicit parameter and functions have no side effects. 2. It introduces ReactiveCocoa as an open source FRP framework for iOS and OSX that uses signals to send values over time and chains signals to transform data values. 3. It explains common functional programming building blocks like map, reduce, and filter that are used to transform and filter signal values in ReactiveCocoa.

1. Quiz 1
1

2. Quiz 2

3. ReactiveCocoa 101
Hai Feng Kao

4. Imperative Programming

5. Object-Oriented Programming
● 封裝、繼承、多型

6. 禪師-鈴木俊隆

7. Why is debugging difficult?

8. Functional Programming
● Lambda Calculus
● Functions without side
effects
● Programs as function
compositions (y =
f(g(h(x))))

9. Functional Reactive Programming
● In functional programming, things get
hard because functions can’t have side-
effects
o Every time a function is called, it must
return the same y for same x
o y = f(x)
● In functional reactive programming, time
is an implicit parameter (no monads)
o y = f(x, t)

10. ReactiveCocoa
● A open source FRP framework
developed by Github
o iOS / OSX
o MIT License
o 3.0 supports swift
o https://github.com/ReactiveCocoa/Re
activeCocoa

11. Signals
● Primary data source of FRP
● Signals send values over time until they
complete
o A signal never sends anything after
completing or erring
o A signal either completes, or errors
out, but never both

12. Signals(cont.)
● A signal has no concept of a “current
value” or “past value”
● It’s like a pipe
● Signals can be chained to transform
the values
o This is core to FRP: data
transformation of values sent over
time

13. KVO Example

14. Reactive Example

15. RACSignals
● always send id, not primitives
o NSInteger -> NSNumber
o CGRect -> NSValue

16. Functional Programming
● The building blocks of functional world
o map, reduce, filter

17. Map
● Mapping performs a value
transformation on the given signal
o It ”maps” each value sent along the
signal to a new value
o It then passes that new value along,
creating a new signal

18. Example

19. ● Combines two or more signals’ values
into one
o Useful for waiting for conditions to be
met
o Useful for deciding between values
Reduce

20. Example

21. Map Reduce Algorithm

22. Map Reduce Algorithm

23. Functional Programming
● The building blocks of functional world
o map, reduce, filter

24. Filter
● Filtering allows values that pass some
test to “pass through”

25. Example

26. Functional Programming
● The building blocks of functional world
o map, reduce, filter

27. Functional Programming
● The building blocks of functional world
o map, reduce, filter
USELESS?

28. Bindings
● Bindings can bind a property to the
latest value sent on a signal
● All bindings created with the RAC
macro are one-way
● Bindings are the secret sauce that hold
apps together

29. Example

30. Demo

31. Imperative vs Functional
Imperative:
Functional:

32. Reference
● Ash Furrow Reactive Cocoa 101
o https://www.youtube.com/watch?v=Tl
gUWYrQ0sc
● Functional Reactive Programming on iOS
o https://leanpub.com/iosfrp/

33. Next Class

34. Next Class

35. Homework

36. Q&A