Laboratory: Prolog (1)

Summary: We begin our exploration of the Prolog programming language.

Prerequisites: Sections 4.1 and 4.2 of Tate. Experience with Linux.

Contents:

• Preparation
• Exercises
  • Exercise 1: Fun with Food
  • Exercise 2: Coloring States
  • Exercise 3: Watching Prolog Compute
  • Exercise 4: Relatives
• For Those with Extra Time

Preparation

Create a directory for the lab.

Exercises

Exercise 1: Fun with Food

a. Try Tate's food example and see if it behaves as advertised.

b. Add the following two rules.

flavor(salty, cracker).
flavor(crunchy, cracker).

Then, determine what flavors a ritz has.

c. Try a few more experiments that you design.

Exercise 2: Coloring States

a. Try Tate's map-coloring example and see if it behaves as advertised.

b. What happens if you don't accept the first result from Prolog? (Keep rejecting results and see what happens.)

Exercise 3: Watching Prolog Compute

Consider the following modification of Tate's food program, which has been extended to print out some information about the rule being applied.

food_type(velveeta, cheese) :- write(rule1), nl.
food_type(ritz, cracker) :- write(rule2), nl.
food_type(spam, meat) :- write(rule3), nl.
food_type(sausage, meat) :- write(rule4), nl.
food_type(jolt, soda) :- write(rule5), nl.
food_type(twinkie, dessert) :- write(rule6), nl.

flavor(sweet, dessert) :- write(rule7), nl.
flavor(savory, meat) :- write(rule8), nl.
flavor(savory, cheese) :- write(rule9), nl.
flavor(sweet, soda) :- write(rule10), nl.

food_flavor(X, Y) :- write(rule11), food_type(X, Z), flavor(Y, Z).

a. Load this file and then try a few queries to see the order in which the Prolog interpreter applies rules.

b. Reverse the order of the two preconditions of food_flavor and see what effect this has on the order in which the Prolog interpreter applies rules.

Exercise 4: Relatives

Here's the start of some rules about a family tree.

related(X,Y) :- ancestor(X,Y).
related(X,Y) :- ancestor(Y,X).
related(X,Y) :- ancestor(Z,Y), ancestor(Z,X).

ancestor(X,Y) :- parent(X,Y).
ancestor(X,Y) :- parent(X,Z), ancestor(Z,Y).

parent(alice,bob).
parent(alice,bill).
parent(andrew,bob).
parent(andrew,bill).
parent(andrew,brianna).
parent(amy,bo).
parent(bob,charles).
parent(billie,charles).
parent(charles,david).
parent(charisma,david).
parent(bo,carlene).
parent(carlene,darlene).

a. Determine all of David's parents.

b. Determine all of Darlene's ancestors.

c. Write some queries of your own.

d. Extend the database.

For Those with Extra Time

Add write and nl predicates to our family database and trace some interesting queries.