gistfile1.txt

Array.class_eval {

 # [1,2,3,4].each_with_previous do |el, prev|
 #   p "el:#{el}, prev:#{prev}"
 # end
 #
 def each_with_previous
   prev = nil
   each do |el|
     yield(el, prev)
     prev = el
   end
 end

}