Continuations in Ruby

Transcript

1. Continuations in Ruby Antono Vasiljev Ruby Open Air, 2012
2. Continuation is basically Rest of the program
3. Continuations are first class objects in Ruby
4. irb(main)> c = callcc { |cont| cont } => #<Continuation:0x7f70ad16d030>
5. Continuations are about Flow Control
6. 1: i = 0 2: callcc do |cont| 3: i = 1 4: cont.call 5: i = 2 # skipped 6: end 7: 8: # i => 1
7. 1: i = 0 2: i = callcc do |cont| 3: i = 1 4: cont.call(2) 5: i = 3 # skipped 6: end 7: 8: # i => 2 # See lines: 2, 4
8. 1| i = 0 2| 3| label :sum 4| 5| puts i += 1 6| 7| goto :sum, cond: (i < 10)
9. 1| LABELS = {} 2| 3| def label(name) 4| callcc { |cont| LABELS[name] = cont } 5| end 6| 7| def goto(label, args: {}) 8| LABELS[label].call if args[:cond] 9| end
10. Continuation are like goto with parameters (but jumps only backward)
11. continuations jumps far def foo bar end def bar baz end def baz $cont[0] end callcc { |c| $cont = c; foo }
12. Similar to exceptions. But can go down through stack. Time Machine!
13. Restartable Exceptions
14. 1| begin 2| hello 3| rescue Exception => e 4| e.restart 5| ensure 6| e.cleanup 7| end
15. 1| def hello 3| i = 0 4| restartable do 5| puts i += 1 6| raise Exception unless i == 5 7| end 8| end
16. 1| def restartable 2| cont = callcc { |c| c } 3| begin 4| yield 5| rescue Exception => e 6| e.continuation = cont 7| raise e 8| end 9| end
17. require 'continuation' class Exception class << self attr_accessor :conts end def continuation=(cont) self.class.conts ||= {} self.class.conts[self.class] ||= cont end
18. def restart self.class.conts[self.class].call end def cleanup self.class.conts.delete(self.class) end end
19. You can do with continuation: Generator objects Fibers/Coroutines Exit from recursion Other control structures
20. Thanks!
21. http://antono.info/