map_e.rb

class Array
  def map_e(elz, &block)
    results = []
    if length > 0
      each do |o|
        block.call(o)
      end
    else
      elz.call
    end
  end
end

# Ruby 1.9-style lambdas make this read a little better
puts %w{dog cat zebra}.map_e(-> { 'No animals!' }) { |o| o.upcase }
puts [].map_e(->{ 'No animals' }) { |o| o.upcase }