Variables

• Clips uses lists for its variables. They call them facts.
• So, you define a fact by for instance a 3-ary predicate like:
  (age-of Chris 52).
• The developer and the reader knows that the age of Chris is 52, when he sees this fact.
• It doesn't matter how many you have.
• If the facts are involved in rules you can use variables with a ? in front of them.
• So (age-of ?X 52) matches any fact like (age-of Chris 52) including (age-of Ian 52)
• So, here's an example rule:
• if (Feature ?X colour green) and (Feature ?X type fruit) then (Feature ?X subtype Watermelon)