[22:56:37][qrush:~/Dev/ruby/memo]
$ irb
irb(main):001:0> load 'fibonacci.rb'
=> true
irb(main):002:0> test_fib
=> 12586269025
irb(main):003:0> exit

[22:56:50][qrush:~/Dev/ruby/memo]
$ rbx
irb(main):001:0> load 'fibonacci.rb'
=> true
irb(main):002:0> test_fib
NameError: undefined local variable or method `memoize' for main
   from Kernel(Object)#memoize (method_missing_cv) at kernel/core/kernel.rb:648
   from Memoize(Object)#memoize {} at /Users/qrush/Dev/rubinius/tmp/gems/1.8/gems/memoize-1.2.3/lib/memoize.rb:11
   from BlockEnvironment#call_on_instance at kernel/core/block_environment.rb:104
   from Object#test_fib at ./fibonacci.rb:12
   from Object#irb_binding {} at (irb):2
irb(main):003:0> exit