gistfile1.rbx

class WhyWeNeedProcs

  def initialize
    @multiplier = lambda { |n| n }
  end

  def multiply( m, &multiplier )
    if block_given?
      # Note the use of & in the method specification explicitly
      # converts any block passed to the method into a proc assigned
      # to the local variable "multiplier"
      @multiplier = multiplier
    end

    @multiplier[m]
  end

end

wwnp = WhyWeNeedProcs.new

puts wwnp.multiply( 5 )

puts wwnp.multiply( 5 ) { |n| 2*n }

puts wwnp.multiply( 10 )