Merge sort implemented in Ruby

merge-sort.rb

def merge_sort(m)
  if m.length <= 1
    return m  
  end
  middle = m.length / 2 - 1
  left = m[0..middle]
  right = m[middle+1..m.length]
  left = merge_sort(left)
  right = merge_sort(right)
  if left.last > right.first
    result = merge(left, right)
  else
    result = left.concat(right)
  end
  return result
end

def merge(left, right)
  result = []
  while left.length > 0 and right.length > 0
    if left.first <= right.first
      result << left.shift      
    else
      result << right.shift
    end    
  end
  if left.length > 0
    result.concat(left)
  else
    result.concat(right)
  end
  return result
end

begin
  list = [1,4,5,7,8,56,32,32,43,43545,67676,324343,5435,0,12,333,3,3,2,1,134,45,7]
  tmp = merge_sort(list)
  puts tmp.inspect
end