def with_current_time
  yield Time.now
end

with_current_time do |now|
  puts now.to_s
end

with_current_time do
  puts 'Hi'
end

with_current_time do |now, hogehoge|
  puts hogehoge.inspect
end

def default_argument_for_block
  yield
end

default_argument_for_block do |val = 'Hi'|
  puts val
end

def flexible_arguments_for_block
  yield 1, 2, 3
end

flexible_arguments_for_block do |*params|
  puts params.inspect
end

def block_sample(&block)
  puts 'stand up'
  block.call if block
  puts 'sit down'
end

block_sample do 
  puts 'hoge'
  puts 'fuga'
end

block_sample