An expert system to pack grocery bags at supermarket checkouts. The task can be broken down into four major stages:

1. Check what the customer has selected, looking over the groceries to see if something may be missing with a view towards suggesting additions to the customer.
2. Bag the large items, with special attention to putting the big bottles in first.
3. Bag the medium items, taking care to put frozen things in freezer bags.
4. Bag the small items, putting them wherever their is room.

Rules

Rule B1 IF step is check-order

there is bag of potato chips

there is no soft drink bottle

THEN add one bottle of Pepsi to order

Rule B2 IF step is check-order

THEN discontinue check-order-step

start bag-large-items step

Rule B3 IF step is bag-large-items

there is large item to be bagged

there is large bottle to be bagged

there is bag with less than 6 large items

THEN put large item in bag

Rule B4 IF step is bag-large-items

there is large item to be bagged

there is bag with less than 6 large items

THEN put large item in bag

Rule B5 IF step is bag-large-items

there is large item to be bagged

THEN start fresh bag

Rule B6 IF step is bag-large-items

THEN discontinue bag-large-items

start bag-medium-items step

Rule B7 IF step is bag-medium-items

there is medium item to be bagged

there is empty bag or bag with medium items

bag is not yet full

medium item is frozen

medium item is not in freezer bag

THEN put medium item in freezer bag

Rule B8 IF step is bag-medium-items

there is medium item to be bagged

there is empty bag or bag with medium items

bag is not yet full

THEN put medium item in bag

Rule B9 IF step is bag-medium-items

there is medium item to be bagged

THEN start fresh bag

Rule B10 IF step is bag-medium-items

THEN discontinue bag-medium-items

Rule B11 IF step is bag-small-items

there is small item to be bagged

there is bag that is not yet full

bag does not contain bottles

THEN put small item in bag

Rule B12 IF step is bag-small-items

there is small item to be bagged

there is bag that is not yet full

THEN put small item in bag

Rule B13 IF step is bag-small-items

there is small item to be bagged

THEN start fresh bag

Rule B14 IF step is bag-small-items

THEN discontinue bag-small-items

stop