def call_twice
  puts "I'm about to call your block."
  yield
  puts "I'm about to call your block again."
  yield
end

call_twice { puts "Hi, I'm a talking code block." }


def repeat(n)
  if block_given?
    n.times { yield }
  else
    raise ArgumentError.new("I can't repeat a block you don't give me!")
  end
end

repeat(4) { puts "Hello." }

repeat(4)