The Fun in Functional - Speaker Deck

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The Fun in Functional Devon Estes @devoncestes github.com/devonestes

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Warning! ⚠

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Warning! ⚠ I’m going to try and be funny

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“First, make the change easy (warning: this may be hard), then make the easy change.” - Kent Beck

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“First, become Aaron Patterson or Justin Searls (warning: this may be hard), then write the presentation.” - Me

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)

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Ruby, we have a problem…

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Moore’s Law

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Speed Complexity

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Moore’s Law is Dead ☠

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Moore’s Law is Dead ☠ (to Ruby)

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Moore’s Law is Dead ☠ (to Ruby) (and by Ruby, I mean MRI)

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Functional Programming to the Rescue!

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Functional Programming to the Rescue! Immutable data structures

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Functional Programming to the Rescue! Immutable data structures Lazy or delayed evaluation

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Functional Programming to the Rescue! Immutable data structures Lazy or delayed evaluation Pure functions

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Functional Programming to the Rescue! Immutable data structures Lazy or delayed evaluation Pure functions Higher order functions

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Functional Programming to the Rescue! Immutable data structures Lazy or delayed evaluation Pure functions Higher order functions Curried functions

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Functional Programming to the Rescue! Immutable data structures Lazy or delayed evaluation Pure functions Higher order functions Curried functions

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Ruby to the Rescue!

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Ruby to the Rescue! Immutable data structures

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Ruby to the Rescue! Immutable data structures Lazy or delayed evaluation

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Ruby to the Rescue! Immutable data structures Lazy or delayed evaluation Pure functions

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Ruby to the Rescue! Immutable data structures Lazy or delayed evaluation Pure functions Higher order functions

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Ruby to the Rescue! Immutable data structures Lazy or delayed evaluation Pure functions Higher order functions Curried functions

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Ruby - The Language of the Future

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I ❤ # => ruby client.rb data_for_team 'New York Jets' # # => ruby client.rb data_for_game 'New York Jets' 'Miami Dolphins' '11/06/2016' # client = NFLData::Client.new(api_key: ENV['NFL_API_KEY']) case ARGV[0] when 'data_for_team' puts client.data_for_team(team_name: ARGV[1]) when 'data_for_game' puts client.data_for_game(team1: ARGV[1], team2: ARGV[2], date: ARGV[3]) else 'Not a recognized command' end

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module NFLData class Client def initialize(api_key:) @api_key = api_key end def data_for_team(team_name:) url = "http://nfl.com/api/v1/teams/#{team_name}?api_key=#{api_key}" raw = fetch_raw_data(url) add_turnover_data(raw) add_win_percentage(raw) add_how_team_is_doing(raw) end def data_for_game(team1:, team2:, date:) url = “http://nfl.com/api/v1/games/#{date}?teams=#{team1},#{team2} &api_key=#{api_key}" raw = fetch_raw_data(url) add_rushing_comparison(raw) add_passing_comparison(raw) end private # ...

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private attr_reader :api_key def fetch_raw_data(url) uri = URI.parse(url) json = Net::HTTP.get(uri) JSON.parse(json) end def add_turnover_data(raw) raw[:turnover_differential] = raw[:num_defensive_turnovers].to_i - raw[:num_offensive_turnovers].to_i end def add_win_percentage(raw) total_games = raw[:num_wins] + raw[:num_losses] raw[:win_percentage] = raw[:num_wins].to_f / total_games.to_f end def add_how_team_is_doing(raw) def add_rushing_comparison(raw) def add_passing_comparison(raw) end end

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team_client = NFLData::Team.new(api_key: ENV['NFL_API_KEY']) game_client = NFLData::Game.new(api_key: ENV['NFL_API_KEY']) case ARGV[0] when 'data_for_team' puts team_client.get_data(team_name: ARGV[1]) when 'data_for_game' puts game_client.get_data(team1: ARGV[1], team2: ARGV[2], date: ARGV[3]) else 'Not a recognized command' end

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module NFLData class Base def initialize(api_key:) @api_key = api_key end private attr_reader :api_key def fetch_raw_data(url) uri = URI.parse(url) json = Net::HTTP.get(uri) JSON.parse(json) end end end

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module NFLData class Game < NFLData::Base def get_data(team1:, team2:, date:) url = “http://nfl.com/api/v1/games/#{date}?teams=#{team1},#{team2} &api_key=#{api_key}" @raw = fetch_raw_data(url) add_rushing_comparison add_passing_comparison add_defensive_comparison end private attr_reader :raw def add_rushing_comparison def add_passing_comparison def add_defensive_comparison end end

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module NFLData class Team < NFLData::Base def get_data(team_name:) url = "http://nfl.com/api/v1/teams/#{team_name}?api_key=#{api_key}" @raw = fetch_raw_data(url) add_turnover_data add_win_percentage add_how_team_is_doing end private attr_reader :raw def add_turnover_data def add_win_percentage def add_how_team_is_doing end end

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45678

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module NFLData class Base def initialize(api_key:, fetcher:) @api_key = api_key @fetcher = fetcher end private attr_reader :api_key, :fetcher end end

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module NFLData class Game < NFLData::Base def call(team1:, team2:, date:) url = "http://nfl.com/api/v1/games/#{date}?teams=#{team1},#{team2} &api_key=#{api_key}" @raw = fetcher.call(url) add_rushing_comparison add_passing_comparison add_defensive_comparison end private attr_reader :raw def add_rushing_comparison def add_passing_comparison def add_defensive_comparison end end

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irb(main):001:0> l = ->(str) { puts str.upcase } irb(main):002:0> l.call('hi') HI nil irb(main):003:0> str = 'hi' irb(main):004:0> p = Proc.new { puts str.upcase } irb(main):005:0> p.call HI nil irb(main):006:0> def up(str) irb(main):007:1> puts str.upcase irb(main):008:1> end :up irb(main):009:0> m = method(:up) Object#upp(str) irb(main):010:0> m.call('hi') HI nil irb(main):011:0> def call_block(&block) irb(main):012:1> block.call('hi') irb(main):013:1> end :call_block irb(main):014:0> call_block { |str| puts str.upcase } HI nil

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fetcher = -> (url) do uri = URI.parse(url) json = Net::HTTP.get(uri) JSON.parse(json) end team_client = NFLData::Team.new(api_key: ENV['NFL_API_KEY'], fetcher: fetcher) game_client = NFLData::Game.new(api_key: ENV['NFL_API_KEY'], fetcher: fetcher) case ARGV[0] when 'data_for_team' puts team_client.get_data(team_name: ARGV[1]) when 'data_for_game' puts game_client.get_data(team1: ARGV[1], team2: ARGV[2], date: ARGV[3]) else 'Not a recognized command' end

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client = NFLData::Client.new(api_key: ENV['NFL_API_KEY']) case ARGV[0] when 'data_for_team' puts client.data_for_team(team_name: ARGV[1]) when 'data_for_game' puts client.data_for_game(team1: ARGV[1], team2: ARGV[2], date: ARGV[3]) else 'Not a recognized command' end

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The Method Object

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module NFLData class Client def initialize(api_key:, fetcher: default_fetcher) @api_key = api_key @fetcher = fetcher end def data_for_team(team_name:) url = "http://nfl.com/api/v1/teams/#{team_name}?api_key=#{api_key}" NFLData::Team.new(fetcher: fetcher).call(url: url) end def data_for_game(team1:, team2:, date:) url = “http://nfl.com/api/v1/games/#{date}?teams=#{team1},#{team2} &api_key=#{api_key}" NFLData::Game.new(fetcher: fetcher).call(url: url) end private attr_reader :api_key, :fetcher def default_fetcher end end

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module NFLData class Game def initialize(fetcher:) @fetcher = fetcher end def call(url:) @data = fetcher.call(url) add_rushing_comparison add_passing_comparison add_defensive_comparison data end private attr_reader :fetcher, :data def add_rushing_comparison def add_passing_comparison def add_defensive_comparison end end

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module NFLData class Team def initialize(fetcher:) @fetcher = fetcher end def call(url:) @data = fetcher.call(url) add_turnover_data add_win_percentage add_how_team_is_doing data end private attr_reader :fetcher, :data def add_turnover_data def add_win_percentage def add_how_team_is_doing end end

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Pure Function

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Pure Function 1) Same output for a given input ⚖

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Pure Function 1) Same output for a given input ⚖ 2) No side effects

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Pure Function Benefits

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Pure Function Benefits Super easy to test

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Pure Function Benefits Super easy to test Super easy to make thread safe

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Pure Function Benefits Super easy to test Super easy to make thread safe Highly composable

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Is it Pure?

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IO#read irb(main):001:0> IO.read('call.rb') "irb(main):001:0> l = ->(str) #..."

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IO#read irb(main):001:0> IO.read('call.rb') "irb(main):001:0> l = ->(str) #..." irb(main):002:0> IO.read('call.rb') Errno::ENOENT: No such file or directory @ rb_sysopen - call.rb from (irb):2:in 'read' from (irb):2 from /Users/devoncestes/.rbenv/versions/2.3.1/bin/irb:11:in ''

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Integer#+ irb(main):001:0> 2 + 2 4

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Integer#+ irb(main):001:0> 2 + 2 4 irb(main):002:0> 2 + 2 4

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Integer#+ irb(main):001:0> 2 + 2 4 irb(main):002:0> 2 + 2 4 irb(main):003:0> 2 + 2 4

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String#downcase irb(main):001:0> str = 'I am a String' "I am a String"

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String#downcase irb(main):001:0> str = 'I am a String' "I am a String" irb(main):002:0> str.downcase "i am a string"

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String#downcase irb(main):001:0> str = 'I am a String' "I am a String" irb(main):002:0> str.downcase "i am a string" irb(main):003:0> str "I am a String"

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String#<< irb(main):001:0> str = 'Is << pure?' "Is << pure?"

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String#<< irb(main):001:0> str = 'Is << pure?' "Is << pure?" irb(main):002:0> str << " Let's find out!" "Is << pure? Let's find out!"

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String#<< irb(main):001:0> str = 'Is << pure?' "Is << pure?" irb(main):002:0> str << " Let's find out!" "Is << pure? Let's find out!" irb(main):003:0> str "Is << pure? Let's find out!"

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client = NFLData::Client.new(api_key: ENV['NFL_API_KEY']) case ARGV[0] when 'team_data' puts client.team_data(team_name: ARGV[1]) when 'game_data' puts client.game_data(team1: ARGV[1], team2: ARGV[2], date: ARGV[3]) else 'Not a recognized command' end

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module NFLData class Client def initialize(api_key:, fetcher: default_fetcher) @api_key = api_key @fetcher = fetcher end def team_data(team_name:, metadata_adder: NFLData::Metadata::Team) url = "http://nfl.com/api/v1/teams/#{team_name}?api_key=#{api_key}" data = fetcher.call(url) metadata_adder.call(data: data) end def game_data(team1:, team2:, date:, metadata_adder: NFLData::Metadata::Game) url = “http://nfl.com/api/v1/games/#{date}?teams=#{team1},#{team2} &api_key=#{api_key}" data = fetcher.call(url) metadata_adder.call(data: data) end private attr_reader :api_key, :fetcher def default_fetcher end end

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module NFLData module Metadata class Team def self.call(**args) new(args).call end def initialize(data:) @data = data end def call add_turnover_data add_win_percentage add_how_team_is_doing data.freeze end private attr_reader :data # ... end end end

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module NFLData module Metadata class Game def self.call(**args) new(args).call end def initialize(data:) @data = data end def call add_rushing_comparison add_passing_comparison add_defensive_comparison data.freeze end private attr_reader :data # ... end end end

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Takeaways

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Takeaways Method objects are your friend

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Takeaways Method objects are your friend Avoid the mystery guest

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Takeaways Method objects are your friend Avoid the mystery guest Look for pure functions ✨

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Takeaways Method objects are your friend Avoid the mystery guest Look for pure functions ✨ Delay and group side effects

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Takeaways Method objects are your friend Avoid the mystery guest Look for pure functions ✨ Delay and group side effects Start thinking about the future

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Grazie mille per l'ascolto! Chi ha domande?