0.1.1.2.3....infinity recursively

fibonacci.rb

class Integer
def fibonacci
  if self < 0
    "Must be a positive number"
  elsif self == 0
    0
  elsif self == 1
    1
  else
   return (self - 1).fibonacci + (self - 2).fibonacci
  end
end
end

puts "'#{8.fibonacci}' should equal '21'"
puts "'#{1.fibonacci}' should be '1'"
puts "'#{2.fibonacci}' should be '1'"
puts "'#{3.fibonacci}' should be '2'"
puts "'#{4.fibonacci}' should be '3'"
puts "'#{0.fibonacci}' should be '0'"