FRiPpery

Talk on functional reactive programming, given at Ruby Manor 4.0.

If you weren’t there, I’m afraid this deck won’t be much use, as some of the slides had screen recordings of the terminal—you’ll have to wait for the video to go up to see those.

Transcript

1. FRiPpery Sunday, 7 April 13
2. WARNING Sunday, 7 April 13
3. Functional Reactive Programming Sunday, 7 April 13
4. Input: Text on STDIN, HTTP request, clicking a button. Output: Text on STDOUT, HTTP response, showing an alert. Sunday, 7 April 13
5. Imperative Ruby • Consuming input IO#read, event handlers, controller actions • Program state: mutable variables, ivars, mutable arrays/hashes • Producing output IO#write, API methods, render() Sunday, 7 April 13
6. FRP • Consuming input: streams • Program state: streams • Producing output: streams Sunday, 7 April 13
7. A stream is an object that emits values. Sunday, 7 April 13
8. Streams can be constructed from other streams. Sunday, 7 April 13
9. Streams are a bit like arrays. • map (a.k.a. collect) - do something with all the elements • select - give me some of the elements Sunday, 7 April 13
10. 1 2 3 4 5 s 2 4 6 8 10 s.map  {|x|  x*2  } Time Sunday, 7 April 13
11. s s.select(&:odd?) Time 1 3 5 1 2 3 4 5 Sunday, 7 April 13
12. s s.scan(0)  {|sum,x|    sum  +  x } Time 1 2 3 4 0 1 3 6 10 Sunday, 7 April 13
13. 1 2 3 s a b t s.merge(t) 1 a 2 3 b Time Sunday, 7 April 13
14. github.com/aanand/wick gem  install  wick Sunday, 7 April 13
15. Sunday, 7 April 13
16. total  =  0   while  line  =  gets    if  line.strip.empty?        puts  "Total:  #{total}\n\n"        total  =  0    else        total  +=  line.to_f    end end Imperative Sunday, 7 April 13
17. require  'wick/io'                                                                                                                               Wick::IO.bind(read:  $stdin,  write:  $stdout)  do  |input|                                                    initial  =  {total:  0}        state  =  input.scan(initial)  {  |s,  line|                                                                                  if  line.strip.empty?            {total:  0,  message:  "Total:  #{s[:total]}"}        else            {total:  s[:total]  +  line.to_f}        end    }        output  =  state.select  {  |s|  s.has_key?(:message)  }                                .map        {  |s|  s[:message]  +  "\n\n"  }      output end Reactive Sunday, 7 April 13
18. input total:  0 state input.scan(initial)  {    ... } output state.filter  {...}          .map        {...} Sunday, 7 April 13
19. total:  1.0 "1" Sunday, 7 April 13
20. total:  3.0 "2" Sunday, 7 April 13
21. total:  0 message:  "Total:  3.0" "" "Total:  3.0\n\n" Sunday, 7 April 13
22. total:  1.0 "1" Sunday, 7 April 13
23. total:  3.0 "2" Sunday, 7 April 13
24. total:  6.0 "3" Sunday, 7 April 13
25. total:  0 message:  "Total:  6.0" "" "Total:  6.0\n\n" Sunday, 7 April 13
26. Build the structure scan select map Sunday, 7 April 13
27. scan select map Connect it to the outside world $stdin $stdout Sunday, 7 April 13
28. Sunday, 7 April 13
29. require  'socket'   socket  =  TCPSocket.new(ARGV[0],  ARGV[1]  ||  23)   begin    while  true        ready  =  IO.select([$stdin,  socket])        ready[0].each  do  |io|            data  =  io.read_nonblock(1_000_000)  #YOLO              if  io.equal?($stdin)                socket.write(data)            elsif  io.equal?(socket)                $stdout.write(data)            end        end    end rescue  EOFError    puts  "A  stream  was  closed.  Shutting  down." end Imperative Sunday, 7 April 13
30. require  'wick/io' require  'socket'     socket  =  TCPSocket.new(ARGV[0],  ARGV[1]  ||  23)                                                                         Wick::IO.bind(      read:    [socket,  $stdin],    write:  [socket,  $stdout]   )  do  |network_in,  user_in|    network_out,  user_out  =  user_in,  network_in    [network_out,  user_out]   end Reactive Sunday, 7 April 13
31. Build the structure Sunday, 7 April 13
32. Connect it to the outside world $stdin $stdout socket (r) socket (w) Sunday, 7 April 13
33. Let’s aim higher. Sunday, 7 April 13
34. Sunday, 7 April 13
35. Sunday, 7 April 13
36. Sunday, 7 April 13
37. Wick::IO.bind(      [socket,  $stdin],    [socket,  $stdout]   )  do  |network_in,  user_in|      #  ...create  network_out  and  user_out...      [network_out,  user_out]   end Sunday, 7 April 13
38. server_events  =  network_in.map  {  |line|  IRCEvent.parse(line)  }             client                    =  Client.new(nick) client_commands  =  client.transform(server_events) network_out          =  user_in.merge(client_commands) Client Sunday, 7 April 13
39. class  Client  <  Struct.new(:nick)    def  transform(server_events)        nick_and_user  =  Wick.from_array([            "NICK  #{nick}",            "USER  #{nick}  ()  *  #{nick}"        ])                    ping  =  server_events.select  {  |msg|  msg.command  ==  "PING"  }                                      pong  =  ping.map  {  |msg|  "PONG  "  +  msg.params.join("  ")  }                                                    nick_and_user.merge(pong)    end       end Client Sunday, 7 April 13
40. ui              =  UI.new user_out  =  ui.transform(client_commands,  server_events) UI Sunday, 7 April 13
41. class  UI    def  transform(client_commands,  server_events)        incoming_messages  =  server_events.select  {  |event|            event.command  ==  "PRIVMSG"        }        other_events  =  server_events.select  {  |event|            event.command  !=  "PRIVMSG"        }          message_lines  =  incoming_messages.map  {  |event|            channel  =  event.params[0]            user        =  "<#{event.user}>"            message  =  event.params[1]              "#{channel.green}  #{user.yellow}  #{message}"        }          message_lines            .merge(other_events.map  {  |event|  "<  #{event.line}".magenta  })            .merge(client_commands.map  {  |line|  ">  #{line}".magenta  })    end end UI Sunday, 7 April 13
42. Sunday, 7 April 13
43. Sunday, 7 April 13
44. Sunday, 7 April 13
45. network_in user_in network_out user_out server_events Client client_commands UI Data Dependency Graph Sunday, 7 April 13
46. Let’s aim higher. Sunday, 7 April 13
47. Sunday, 7 April 13
48. Sunday, 7 April 13
49. network_in user_in network_out user_out Client UI server_events user_commands Sunday, 7 April 13
50. class  Client    def  transform(network_in,  user_commands)        server_events  =  network_in.map  {  |line|  IRCEvent.parse(line)  }          nick_and_user  =  Wick.from_array([            "NICK  #{nick}",            "USER  #{nick}  ()  *  #{nick}"        ])          ping  =  server_events.select  {  |msg|  msg.command  ==  "PING"  }        pong  =  ping.map  {  |msg|  "PONG  "  +  msg.params.join("  ")  }          outgoing  =  process_user_commands(user_commands)          network_out  =  outgoing.merge(nick_and_user).merge(pong)          [network_out,  server_events]    end end Sunday, 7 April 13
51. class  Client    def  transform(network_in,  user_commands)        server_events  =  network_in.map  {  |line|  IRCEvent.parse(line)  }          nick_and_user  =  Wick.from_array([            "NICK  #{nick}",            "USER  #{nick}  ()  *  #{nick}"        ])          ping  =  server_events.select  {  |msg|  msg.command  ==  "PING"  }        pong  =  ping.map  {  |msg|  "PONG  "  +  msg.params.join("  ")  }          outgoing  =  process_user_commands(user_commands)          network_out  =  outgoing.merge(nick_and_user).merge(pong)          [network_out,  server_events]    end end Sunday, 7 April 13
52. class  Client    def  transform(network_in,  user_commands)        server_events  =  network_in.map  {  |line|  IRCEvent.parse(line)  }          nick_and_user  =  Wick.from_array([            "NICK  #{nick}",            "USER  #{nick}  ()  *  #{nick}"        ])          ping  =  server_events.select  {  |msg|  msg.command  ==  "PING"  }        pong  =  ping.map  {  |msg|  "PONG  "  +  msg.params.join("  ")  }          outgoing  =  process_user_commands(user_commands)          network_out  =  outgoing.merge(nick_and_user).merge(pong)          [network_out,  server_events]    end end Sunday, 7 April 13
53. def  process_user_commands(user_commands)    user_commands.map  {  |cmd|        case  cmd.action        when  nil            if  cmd.channel                "PRIVMSG  #{cmd.channel}  :#{cmd.argument}"            else                cmd.argument            end        when  :join            "JOIN  #{cmd.channel}"        when  :part            "PART  #{cmd.channel}"        when  :quit            "QUIT  :#{cmd.argument}"        else            nil        end    }.compact end Sunday, 7 April 13
54. UI Sunday, 7 April 13
55. ChannelState  =  Struct.new(:joined_channels,  :current_index)   #  initial  state ChannelState.new([],  nil)   #  after  joining  rubymanor ChannelState.new(["#rubymanor"],  0)   #  after  joining  cats  and  dogs ChannelState.new(["#rubymanor",  "#cats",  "#dogs"],  2)   #  after  typing  "/prev" ChannelState.new(["#rubymanor",  "#cats",  "#dogs"],  1) Sunday, 7 April 13
56. class  ChannelState    def  update_channel_index(inc)        ChannelState.new(            joined_channels,            (channel_index  +  inc)  %  joined_channels.length)    end      def  join_channel(name)        new_list  =  joined_channels  |  [name]        new_idx    =  new_list.length-­‐1          ChannelState.new(new_list,  new_idx)    end      def  part_channel(name)        new_list  =  joined_channels  -­‐  [name]        new_idx    =  [channel_index,  new_list.length-­‐1].min          ChannelState.new(new_list,  new_idx)    end end Sunday, 7 April 13
57. def  get_channel_state(user_commands,  server_events)    initial_state  =  ChannelState.new([],  nil)      manual_changes        =  get_manual_state_changes(user_commands)    automatic_changes  =  get_automatic_state_changes(server_events)    all_changes              =  manual_changes.merge(automatic_changes)      all_changes.scan(initial_state)  {  |state,  change|  ...  } end Sunday, 7 April 13
58. def  get_manual_state_changes(user_commands)    user_commands        .select  {  |cmd|            cmd.action  ==  :next  or  cmd.action  ==  :prev        }        .map  {  |cmd|            if  cmd.action  ==  :next                [:update_channel_index,  +1]            elsif  cmd.action  ==  :prev                [:update_channel_index,  -­‐1]            end                  }         end Sunday, 7 April 13
59. def  get_automatic_state_changes(server_events)    server_events        .select  {  |event|            event.command  ==  "JOIN"  or  event.command  ==  "PART"        }        .map  {  |event|            if  event.command  ==  "JOIN"                channel  =  event.params.first                [:join_channel,  channel]            elsif  event.command  ==  "PART"                channel  =  event.params.first                [:part_channel,  channel]            end        } end Sunday, 7 April 13
60. all_changes.scan(initial_state)  {  |state,  change|    if  change.first  ==  :update_channel_index        state.update_channel_index(change.first,  change.last)    elsif  change.first  ==  :join_channel        state.join_channel(change.first,  change.last)    elsif  change.first  ==  :part_channel        state.part_channel(change.first,  change.last)    end } Sunday, 7 April 13
61. all_changes.scan(initial_state)  {  |state,  change|    state.send(change.first,  change.last) } Sunday, 7 April 13
62. THIS IS FAFF Sunday, 7 April 13
63. NO TO FAFF Sunday, 7 April 13
64. YES TO FUNCTIONS Sunday, 7 April 13
65. def  get_manual_state_changes(user_commands)    user_commands        .select  {  |cmd|            cmd.action  ==  :next  or  cmd.action  ==  :prev        }        .map  {  |cmd|            proc  {  |state|                if  cmd.action  ==  :next                    state.update_channel_index(+1)                elsif  cmd.action  ==  :prev                    state.update_channel_index(-­‐1)                end            }        } end Sunday, 7 April 13
66. def  get_automatic_state_changes(server_events)    server_events        .select  {  |event|            event.command  ==  "JOIN"  or  event.command  ==  "PART"        }        .map  {  |event|            proc  {  |state|                if  event.command  ==  "JOIN"                    state.join_channel(event.params.first)                elsif  event.command  ==  "PART"                    state.part_channel(event.params.first)                end              }              }       end Sunday, 7 April 13
67. all_changes.scan(initial_state)  {  |state,  change|    change.call(state) } Sunday, 7 April 13
68. network_in user_in network_out user_out Client UI server_events user_commands Sunday, 7 April 13
69. network_out,  server_events  =    client.transform(network_in,  user_commands)   user_out,  user_commands  =    ui.transform(user_in,  server_events) Sunday, 7 April 13
70. user_out,  user_commands  =    ui.transform(user_in,  server_events) network_out,  server_events  =    client.transform(network_in,  user_commands) Sunday, 7 April 13
71. server_events_bus  =  Wick::Bus.new user_commands_bus  =  Wick::Bus.new   network_out,  server_events  =    client.transform(network_in,  user_commands_bus)   user_out,  user_commands  =    ui.transform(user_in,  server_events_bus)   server_events_bus.consume!(server_events) user_commands_bus.consume!(user_commands) Sunday, 7 April 13
72. “Do the Dirty Work Outside” Sunday, 7 April 13
73. CONCLUSION Sunday, 7 April 13
74. FRP is weird. FRP is fun. Sunday, 7 April 13
75. FRP forces you to think about stuff. Sunday, 7 April 13
76. Asynchronous APIs Testing strategies Other languages Sunday, 7 April 13
77. Thanks. Have fun. github.com/aanand/wick Sunday, 7 April 13