user_query: add socks to shopping list
response_text: OK, I added socks.
user_query: scratch that add handkerchief instead 
response_text: Sure, I changed the list item to handkerchief on your list called "shopping."
user_query: shopping list
response_text: You have three things on that list.
User: Get some cottage cheese today while at Trader Joe's.
Parse: Get_product ( product « cottage cheese » product_source « Trader Joe's » )