class Object
  def when(*a, &block)
     a.inject(true) {|m, n| m && n} ? block.call(*([self] + a)) : self
  end
end

upper_limit = nil
puts [1, 2, 3, 4, 5].when(upper_limit) {|array, upper_limit| array.select {|e| e < upper_limit}}.map {|n| n ** 2}.inject(0) {|m, n| m + n}
# => 55

# OR

upper_limit = 3
puts [1, 2, 3, 4, 5].when(upper_limit) {|array, upper_limit| array.select {|e| e < upper_limit}}.map {|n| n ** 2}.inject(0) {|m, n| m + n}
# => 5