--- yield(arg ... )

    ruby 1.7 feature

    Proc#call [Proc/call] ƱǤοΥåԤޤ

        pr = Proc.new {|a,b,c| p [a,b,c]}
        pr.yield(1)        #=> [1, nil, nil]
        pr.yield(1,2,3,4)  #=> [1, 2, 3]
        pr.call(1)         #=> wrong # of arguments (4 for 3) (ArgumentError)


     yield ƱưǤ

        def foo
          yield(1)
        end
        foo {|a,b,c| p [a,b,c]}

