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: add handkerchief 
Parse: Add_item_to_list ( items « handkerchief » )