From: Daniel Schierbeck <daniel.schierbeck@...>
Date: 2005-09-15T23:31:35+09:00
Subject: Math: sum and faculty

I hereby propose two additions to Ruby. Please come with some comments 
before I file an RCR.


Range#sum
=========

Usage
-----

   (lower_limit..upper_limit).sum { |i| expression }


Implementation
--------------

   class Range
     def sum
       raise ArgumentError unless block_given?

       result = 0.0
       each { |i| result += yield(i) }

       result
     end
   end


Notes
-----

Could also be implemented as Math#sum



Integer#faculty
===============

Usage
-----

   n.faculty # => n * (n - 1) * (n - 2) ... 1


Implementation
--------------

   class Integer
     def faculty
       self == 0 ? 1 : self * (self - 1).faculty
     end
   end




Cheers,
Daniel