regex_with_fibers.rb

#!/usr/bin/env ruby

require 'fiber'

# This state machine corresponds to the regular expression /ab*(c|d)/

@start = Fiber.new do
  loop do
    case (@string.next rescue nil)
    when 'a' then @state1.transfer
    else @errorstate.transfer
    end
  end
end

@state1 = Fiber.new do
  loop do
    case (@string.next rescue nil)
    when 'b' then @state1.transfer
    when 'c', 'd' then @endstate.transfer
    else @errorstate.transfer
    end
  end
end

@endstate = Fiber.new do
  puts "It's a match!"
end

@errorstate = Fiber.new do
  raise ArgumentError, 'String does not match!'
end

@string = 'abbbbb'.chars
@start.transfer