gistfile1.rb

require 'fiber'

def event_callback(letter)
   puts "I've encountered #{letter} !!"
end

f = Fiber.new do
  ('a'..'z').each do |l|
   Fiber.yield(event_callback(l)) if (l == "c" || l == "h")
  end
end

while f.alive? do
   f.resume
end