CS 440 Assert in Prolog July 14, 2008
1 Objectives
You can often tell what the language designers thought about their language by the libraries that are included
with it. Many of Prolog’s involve the analysis of structres. In this lecture we will go over some of the builtin
predicates of Prolog.
•Know how to use call and assert
•Know how to use findall and checklist.
2 Examples
1?- dynamic likes/2.
2?- likes(john,mary).
3No
4?- assert(likes(X,Y) :- likes(Y,X)).
5?- assert(likes(john,mary)).
6?- likes(mary,X).
7ERROR: Out of local stack
8?- retract(likes(john,mary)).
9Yes
10 ?- asserta(likes(john,mary)).
11 Yes
12 ?- likes(mary,X).
13 X = john
3 Problems
Try the following problems. In a few minutes the instructor will go over the solutions. Feel free to work with
the person next to you!
1. Write a function “says” that takes two arguments. The first is the name of a person making the
implication. The second is a prolog expression. Record the claim, and then tell the prolog.
2. Next, suppose we can find out later that some people aren’t reliable, and we should no longer believe
anything they say. Write a function “disbelieve” that takes the name of a person and retracts
everything they said before.
1?- says(frank,likes(john,mary)).
2?- likes(john, mary).
3Yes
4?- disbelieve(frank).
5?- likes(john, mary).
6No
Mattox Beckman Page 1 Illinois Institute of Technology