Fibers - Speaker Deck

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Fibers DENIS DEFREYNE / RUG::B / MARCH 2ND, 2017

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Basics 2

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3 f = lambda do puts "hi" end f.call

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3 f = lambda do puts "hi" end f.call hi

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4 f = Fiber.new do puts "hi" end f.resume

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4 f = Fiber.new do puts "hi" end f.resume hi

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5 f = lambda do puts "hi" end f.call hi

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6 f = lambda do puts "hi" return puts "bye" end f.call

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6 f = lambda do puts "hi" return puts "bye" end f.call hi

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7 f = Fiber.new do puts "hi" return puts "bye" end f.resume

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7 f = Fiber.new do puts "hi" return puts "bye" end f.resume hi

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7 f = Fiber.new do puts "hi" return puts "bye" end f.resume hi sample.rb:3:  in`block in ':  unexpected return  (LocalJumpError)

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8 f = Fiber.new do puts "hi" Fiber.yield puts "bye" end f.resume

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8 f = Fiber.new do puts "hi" Fiber.yield puts "bye" end f.resume hi

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9 f = lambda do puts "hi" end f.call  hi

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10 f = lambda do puts "hi" end f.call f.call

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10 f = lambda do puts "hi" end f.call f.call hi hi

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11 f = Fiber.new do puts "hi" end f.resume f.resume

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11 f = Fiber.new do puts "hi" end f.resume f.resume hi

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11 f = Fiber.new do puts "hi" end f.resume f.resume hi a.rb:6:  in `resume':  dead fiber called  (FiberError)

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12 f = lambda do puts "hi" return puts "bye" end f.call  hi 

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13 f = lambda do puts "hi" return puts "bye" end f.call f.call

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13 f = lambda do puts "hi" return puts "bye" end f.call f.call hi hi

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14 f = Fiber.new do puts "hi" Fiber.yield puts "bye" end f.resume f.resume

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14 f = Fiber.new do puts "hi" Fiber.yield puts "bye" end f.resume f.resume hi bye

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15 Create a fiber Fiber.new { … } Start running a fiber f.resume Resume an running fiber f.resume Return from a fiber Fiber.yield

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16 f = Fiber.new do puts 'hi' end f.resume hi

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17 f = Fiber.new do |a| puts a end f.resume('hi')

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17 f = Fiber.new do |a| puts a end f.resume('hi') hi

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18 f = Fiber.new do |a| puts a    end f.resume('hi')  hi

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19 f = Fiber.new do |a| puts a Fiber.yield puts 'bye' end f.resume('hi') f.resume hi  bye

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20 f = Fiber.new do |a| puts a b = Fiber.yield puts b end f.resume('hi') f.resume('bye')

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20 f = Fiber.new do |a| puts a b = Fiber.yield puts b end f.resume('hi') f.resume('bye') hi bye

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21 f = Fiber.new do puts 'hi' end f.resume hi

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22 f = Fiber.new do 'hi' end puts f.resume

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22 f = Fiber.new do 'hi' end puts f.resume hi

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23 f = Fiber.new do puts 'hi' end f.resume hi 

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24 f = Fiber.new do puts 'hi' Fiber.yield 'bye' end f.resume puts f.resume hi  bye

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25 f = Fiber.new do  Fiber.yield('hi')  'bye' end puts f.resume puts f.resume

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25 f = Fiber.new do  Fiber.yield('hi')  'bye' end puts f.resume puts f.resume hi bye

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26 Create a fiber Fiber.new { … } Start running a fiber f.resume(…) Resume an running fiber f.resume(…) Return from a fiber Fiber.yield(…)

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Five (Practical) Applications 27

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0. Async, non-blocking IO  and maybe reactive things 28

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(Use your imagination here) 29

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1. Inﬁnite lists 30

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31   f = Fiber.new do Fiber.yield(0) Fiber.yield(1) Fiber.yield(2) … end puts f.resume puts f.resume puts f.resume 0 1 2

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32 f = Fiber.new do v = 0 loop do Fiber.yield(v) v += 1 end end puts f.resume puts f.resume puts f.resume 0 1 2

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33 class Ints def initialize @f = Fiber.new { … } end def each loop do yield(@f.resume) end end end

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34 Ints.new.each do |i| puts i end

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34 Ints.new.each do |i| puts i end 0 1 2 3 4 5 6 7 8 9 10 11 12 13

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35 Ints = Enumerator.new do |y| v = 0 loop do y << v v += 1 end end

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(You don’t need fibers for this.) 36

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2. Wizards 37

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38 What is your first name? > Denis Hi, Denis. What is your last name? > Defreyne Got it — Defreyne! Thanks for your help, Denis Defreyne! Bye-bye for now!

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39 first_name = ask "What is your first name?" say "Hi, #{first_name}." last_name = ask "What is your last name?" say "Got it -- #{last_name}!" say "Thanks for your help, #{first_name}!" say "Bye-bye for now!" stop

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40 def ask(s) puts s print '> ' gets.chomp end def say(s) puts s end def stop end

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41 first_name = ask "What is your first name?" say "Hi, #{first_name}." last_name = ask "What is your last name?" say "Got it -- #{last_name}!" say "Thanks for your help, #{first_name}!" say "Bye-bye for now!" stop

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42 wizard = Fiber.new do first_name = ask "What is your first name?" say "Hi, #{first_name}." last_name = ask "What is your last name?" say "Got it -- #{last_name}!" say "Thanks for your help, #{first_name}!" say "Bye-bye for now!" stop end

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43 def ask(s) Fiber.yield(Question.new(s)) end def say(s) Fiber.yield(Statement.new(s)) end def stop Fiber.yield(Stop.new) end

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44 answer = nil loop do instruction = wizard.resume(answer) case instruction when Question when Statement when Stop end end

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45 answer = nil loop do instruction = wizard.resume(answer) case instruction when Question puts instruction.text print '> ' answer = gets.chomp when Statement when Stop end end

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46 answer = nil loop do instruction = wizard.resume(answer) case instruction when Question puts instruction.text print '> ' answer = gets.chomp when Statement puts instruction.text when Stop end end

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47 answer = nil loop do instruction = wizard.resume(answer) case instruction when Question puts instruction.text print '> ' answer = gets.chomp when Statement puts instruction.text when Stop break end end

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We’ve separated what to do (wizard) from how to do it (CLI, GUI, …) 48

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49 pieces = [] answer = nil loop do instruction = wizard.resume(answer) case instruction when Question when Statement when Stop end end

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50 when Question pieces << instruction.text pieces << '' pieces << '' pieces << '' pieces << '' return pieces.join(' ')

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51 when Statement pieces << instruction.text

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52 when Stop return pieces.join(' ')

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3. Resumable exceptions 53

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54 handle_exception do puts 'before' puts Boom.new.throw puts 'after' end.…

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55 handle_exception do puts 'before' puts Boom.new.throw puts 'after' end.on(Boom) do |e| e.resume('exceptional') end.…

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56 handle_exception do puts 'before' puts Boom.new.throw puts 'after' end.on(Boom) do |e| e.resume('exceptional') end.run

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57 handle_exception do puts 'before' puts Boom.new.throw puts 'after' end.on(Boom) do |e| e.resume('exceptional') end.run before exceptional after

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58 handle_exception do puts 'before' puts Boom.new.throw puts 'after' end.run before sample.rb:31:  in `block in run': ohnoes kaboom  (Boom)

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4. Run-time dependencies 59

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60 http://nanoc.ws Nanoc

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63 Create a fiber Fiber.new { … } Start running a fiber f.resume(…) Resume an running fiber f.resume(…) Return from a fiber Fiber.yield(…)

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64 Q&A Find me at @ddfreyne on Twitter, or denis@stoneship.org.