user_query: Add apples from my list of Fruits. 
response_text: Got it. Which list do you want to add to?
user_query: Fruits
response_text: I couldn't find a list called "Fruits." Do you want me to make one?
user_query: yes
response_text: OK, I made a list called "Fruits" and added apples.
User: I'll need um shoes from Walmart.
Parse: Get_product ( product « shoes » product_source « Walmart » )