def call_twice
  puts "Calling your block."
  ret1 = yield("very first")
  puts "The value of your block: #{ret1}"

  puts "Calling your block again."
  ret2 = yield("second")
  puts "The value of your block: #{ret2}"
end

call_twice do |which_time|
  puts "I'm a code block, called for the #{which_time} time."
  which_time == "very first" ? 1 : 2
end