Merge sort ruby

merge_sort.rb

#!/usr/bin/env ruby
# 2011-10-10 20:57:53 +1000

def merge_sort a
    return a if a.size <= 1
    l,r = split_array a
    result = combine merge_sort(l), merge_sort(r)
end

def split_array a
  mid = (a.size/2).round
  return a.take(mid), a[mid, a.size-mid]
end

def combine a, b
  return b.size.zero? ? a : b if a.first.nil? || b.first.nil?
  smallest = a.first <= b.first ? a.shift : b.shift
  return combine(a, b).unshift(smallest)
end

a = [6,23,53,1,2,5,62,61,33,21,14,6,23].shuffle
puts "#{merge_sort(a)}"