--- step([s]) {|item| ... }

    ruby 1.7 feature

    ϰǤ s ˷֤ޤs ˤ
    ꤷޤǥեȤ 1 Ǥ
    

         ("a" .. "f").step(2) {|v| p v}
         # => "a"
              "c"
              "e"

