This document provides an overview of functional programming concepts using Ruby. It discusses some of the problems with object-oriented programming like side effects and sharing of data and code. It then presents some ways to adopt a more functional style in Ruby, such as treating loops and data structures as functions. The document also introduces the Functional Ruby gem which adds features inspired by languages like Erlang and Haskell, including pattern matching, immutability and memoization. Overall, the document aims to demonstrate how functional programming principles can be applied in Ruby.

1. FUNCTIONAL
RUBY

3. ABOUT ME
• Mikhail Bortnyk

4. ABOUT ME
• Mikhail Bortnyk
• Too old for this shit

5. ABOUT ME
• Mikhail Bortnyk
• Too old for this shit
• Work for Amoniac OÜ

6. ABOUT ME
• Mikhail Bortnyk
• Too old for this shit
• Work for Amoniac OÜ
• Ruby developer

7. ABOUT ME
• Mikhail Bortnyk
• Too old for this shit
• Work for Amoniac OÜ
• Ruby developer
• Language researcher

8. ABOUT ME
• Mikhail Bortnyk
• Too old for this shit
• Work for Amoniac OÜ
• Ruby developer
• Language researcher
• kottans.org co-founder

9. ABOUT ME
• Mikhail Bortnyk
• Too old for this shit
• Work for Amoniac OÜ
• Ruby developer
• Language researcher
• kottans.org co-founder
• twitter @mikhailbortnyk

10. LOOK
FOR
JACKIE*
SPECIAL OFFER
*НАЕБЫВАЮ

11. PART ONE
WHY FUNCTIONAL?

12. SIDE EFFECTS
PROBLEM 1.1
• your objects store state

13. SIDE EFFECTS
PROBLEM 1.1
• your objects store state
• your code modifies state

14. SIDE EFFECTS
PROBLEM 1.1
• your objects store state
• your code modifies state
• your other code modifies state too

15. SIDE EFFECTS
PROBLEM 1.1
• your objects store state
• your code modifies state
• your other code modifies state too
• summary: mess

16. SIDE EFFECTS
PROBLEM 1.1
• your objects store state
• your code modifies state
• your other code modifies state too
• summary: mess

17. DATA/CODE ENTITY SHARING
PROBLEM 1.2
• your model stores both your logic and data

18. DATA/CODE ENTITY SHARING
PROBLEM 1.2
• your model stores both your logic and data
• nuff said

19. DATA/CODE ENTITY SHARING
PROBLEM 1.2
• your model stores both your logic and data
• nuff said

20. HYPE
PROBLEM 1.3
• Erlang

21. HYPE
PROBLEM 1.3
• Erlang
• Haskell

22. HYPE
PROBLEM 1.3
• Erlang
• Haskell
• Scala

23. HYPE
PROBLEM 1.3
• Erlang
• Haskell
• Scala
• OCaml

24. HYPE
PROBLEM 1.3
• Erlang
• Haskell
• Scala
• OCaml
• Lisp

25. HYPE
PROBLEM 1.3
• Erlang
• Haskell
• Scala
• OCaml
• Lisp
• Javascript (sic!)

26. HYPE
PROBLEM 1.3
• Erlang
• Haskell
• Scala
• OCaml
• Lisp
• Javascript (sic!)
• Ruby (sic!)

27. PART TWO
EASY (NOT REALLY) LEVEL

28. LIMITS ARE FREEING
CLEAN YOUR RUBY
• David Copeland article “Adventures in functional programming
with Ruby”

29. LIMITS ARE FREEING
CLEAN YOUR RUBY
• David Copeland article “Adventures in functional programming
with Ruby”
• Loops are just functions

30. LIMITS ARE FREEING
CLEAN YOUR RUBY
• David Copeland article “Adventures in functional programming
with Ruby”
• Loops are just functions
• Data structures are just functions

31. LIMITS ARE FREEING
CLEAN YOUR RUBY
• David Copeland article “Adventures in functional programming
with Ruby”
• Loops are just functions
• Data structures are just functions
• Objects are just functions

32. LIMITS ARE FREEING
CLEAN YOUR RUBY
• David Copeland article “Adventures in functional programming
with Ruby”
• Loops are just functions
• Data structures are just functions
• Objects are just functions
• Namespaces are just functions

33. LIMITS ARE FREEING
CLEAN YOUR RUBY
• David Copeland article “Adventures in functional programming
with Ruby”
• Loops are just functions
• Data structures are just functions
• Objects are just functions
• Namespaces are just functions
• P.S. Ruby HAS Tail Call Optimization

34. ROUGH HACK
TAIL-CALL OPTIMIZATION
def fact(n, acc=1)
return acc if n <= 1
fact(n-1, n*acc)
end
RubyVM::InstructionSequence.compile_option = {
tailcall_optimization: true,
trace_instruction: false
}
fact(1000)

35. FUNCTIONAL VS OBJECT-ORIENTED
SIDE TO SIDE COMPARISON
new_person = ->(name, birthdate, gender, title, id=nil) {
return ->(attribute) {
return id if attribute == :id
return name if attribute == :name
return birthdate if attribute == :birthdate
return gender if attribute == :gender
return title if attribute == :title
nil
}
}
class Person
attr_reader :id, :name, :birthdate, :gender, :title
def initialize(name, birthdate, gender, title, id=nil)
@id = id
@name = name
@birthdate = birthdate
@gender = gender
@title = title
end
end

36. SPECIAL KNOWLEDGE
WHAT’S WRONG WITH OO-CODE?
• WTF is “class”

37. SPECIAL KNOWLEDGE
WHAT’S WRONG WITH OO-CODE?
• WTF is “class”
• WTF are .new and initialize

38. SPECIAL KNOWLEDGE
WHAT’S WRONG WITH OO-CODE?
• WTF is “class”
• WTF are .new and initialize
• API of class

39. SPECIAL KNOWLEDGE
WHAT’S WRONG WITH OO-CODE?
• WTF is “class”
• WTF are .new and initialize
• API of class
• WTF are @-variables

40. SPECIAL KNOWLEDGE
WHAT’S WRONG WITH OO-CODE?
• WTF is “class”
• WTF are .new and initialize
• API of class
• WTF are @-variables
• difference between class and instance

41. SPECIAL KNOWLEDGE
WHAT’S WRONG WITH OO-CODE?
• WTF is “class”
• WTF are .new and initialize
• API of class
• WTF are @-variables
• difference between class and instance
• WTF is “attr_reader”

42. NO HIDDEN MAGIC
FUNCTIONAL PROGRAMMING CODE
• how to define function

43. NO HIDDEN MAGIC
FUNCTIONAL PROGRAMMING CODE
• how to define function
• how to call function

44. TO DON’T SHOOT YOUR LEG
SAFETY RULES
• do not modify, create new

45. TO DON’T SHOOT YOUR LEG
SAFETY RULES
• do not modify, create new
• BUY MORE RAM

46. TO DON’T SHOOT YOUR LEG
SAFETY RULES
• do not modify, create new
• BUY MORE RAM
• functions should not depend on environment

47. TO DON’T SHOOT YOUR LEG
SAFETY RULES
• do not modify, create new
• BUY MORE RAM
• functions should not depend on environment
• BUY EVEN MORE RAM

48. TO DON’T SHOOT YOUR LEG
SAFETY RULES
• do not modify, create new
• BUY MORE RAM
• functions should not depend on environment
• BUY EVEN MORE RAM
• avoid returns

49. TO DON’T SHOOT YOUR LEG
SAFETY RULES
• do not modify, create new
• BUY MORE RAM
• functions should not depend on environment
• BUY EVEN MORE RAM
• avoid returns
• use lambdas

50. TO DON’T SHOOT YOUR LEG
SAFETY RULES
• do not modify, create new
• BUY MORE RAM
• functions should not depend on environment
• BUY EVEN MORE RAM
• avoid returns
• use lambdas
• DO NOT FORGET TO ORDER RAM RIGHT NOW

51. SIDE TO SIDE RULES COMPARISON
FUNCTIONAL VS OBJECT-ORIENTED
• how to perform tasks and
how to track changes
• state changes are important
• order of execution is
important
• flow controlled by loops,
conditionals, function calls
• instances of structures and
classes
• focus on what information is
needed and what
transformations required
• state changes are non-existent
• order of execution is low-
important
• flow controlled by function
calls including recursion
• functions are first class
objects, data collections

52. — Greenspun’s tenth rule of programming
ANY SUFFICIENTLY COMPLICATED C OR
FORTRAN PROGRAM CONTAINS AN AD-HOC,
INFORMALLY-SPECIFIED, BUG-RIDDEN, SLOW
IMPLEMENTATION OF HALF OF COMMON LISP.
”
“

53. PART THREE
I AM DEVELOPER, I DON’T WANT
TO LEARN, I WANT PATTERN
MATCHING AND IMMUTABILITY

54. STILL EVOLVING!
FUNCTIONAL-RUBY GEM
• created by Jerry D’Antonio

55. STILL EVOLVING!
FUNCTIONAL-RUBY GEM
• created by Jerry D’Antonio
• inspired by Erlang, Clojure, Haskell and Functional Java

56. STILL EVOLVING!
FUNCTIONAL-RUBY GEM
• created by Jerry D’Antonio
• inspired by Erlang, Clojure, Haskell and Functional Java
• has records, unions and tuples

57. STILL EVOLVING!
FUNCTIONAL-RUBY GEM
• created by Jerry D’Antonio
• inspired by Erlang, Clojure, Haskell and Functional Java
• has records, unions and tuples
• has protocols

58. STILL EVOLVING!
FUNCTIONAL-RUBY GEM
• created by Jerry D’Antonio
• inspired by Erlang, Clojure, Haskell and Functional Java
• has records, unions and tuples
• has protocols
• has Erlang-style pattern matching

59. STILL EVOLVING!
FUNCTIONAL-RUBY GEM
• created by Jerry D’Antonio
• inspired by Erlang, Clojure, Haskell and Functional Java
• has records, unions and tuples
• has protocols
• has Erlang-style pattern matching
• has function memoization

60. STILL EVOLVING!
FUNCTIONAL-RUBY GEM
• created by Jerry D’Antonio
• inspired by Erlang, Clojure, Haskell and Functional Java
• has records, unions and tuples
• has protocols
• has Erlang-style pattern matching
• has function memoization
• supports MRI, JRuby and Rubinius

61. FUNCTIONAL-RUBY GEM
SHORT OVERVIEW

62. PATTERN MATCHING AND TYPE CHECKING
FUNCTIONAL-RUBY GEM
class Yoga
include Functional::PatternMatching
include Functional::TypeCheck
defn(:where_is_sun) do
puts "o"
end
defn(:where_is_sun, 14) do
puts "88!"
end
defn(:where_is_sun, _) do |name|
puts "o, #{name}!"
end
defn(:where_is_sun, _) do |name|
puts "Are you in wrong district, #{name.rude_name}?"
end.when { |name| Type?(name, Moskal) }
defn(:where_is_sun, _, _) do |name, surname|
"o, #{name} #{surname}!"
end
end

63. MEMOIZATION
FUNCTIONAL-RUBY GEM
class Factors
include Functional::Memo
def self.sum_of(number)
of(number).reduce(:+)
end
def self.of(number)
(1..number).select {|i| factor?(number, i)}
end
def self.factor?(number, potential)
number % potential == 0
end
memoize(:sum_of)
memoize(:of)
end

64. RECORDS
FUNCTIONAL-RUBY GEM
Name = Functional::Record.new(:first, :middle, :last, :suffix) do
mandatory :first, :last
default :first, 'J.'
default :last, 'Doe'
end

65. QUESTION

66. Q&A

67. THANK YOU