Go here for a common Lisp program that allows users to teach chatbots how to tell ‘what do you get?’ jokes.

The program basically allows users to seed the generator with knowledge about different objects, and to use that vocabulary to deliver unique jokes.

User: Tell me a joke
Bot: What do you get when you cross a dance with a cheetah?
User: What?
Bot: Fastball

User: Tell me a joke
Bot: What do you get when you cross an alien with a chicken?
User: What?
Bot: Eggs-traterrestrial

And so on…