Programming with Prolog IV

1. CSE240 – Introduction to
Programming Languages
Lecture 25:
Programming with Prolog IV
Javier Gonzalez-Sanchez
javiergs@asu.edu
javiergs.engineering.asu.edu
Office Hours: By appointment

2. Javier Gonzalez-Sanchez | CSE 240 | Fall 2017 | 2
Announcement
• Homework 6 due Nov 29.
• Quiz 9 due Nov 29.

3. Expressions and Recursion

4. Javier Gonzalez-Sanchez | CSE 240 | Fall 2017 | 4
Arithmetic Queries
?- X is 3 + 5.
X=8
?- X is 3 mod 2.
X=1
?- X is 3 mod 2 - 1 * 5 / 9.
X=0.4444444444444444
?- X is 5+4, Y is 5-4.
X=9
Y=1
?- X is 5*4, Y is 2^3.
X=20
Y=8

5. Javier Gonzalez-Sanchez | CSE 240 | Fall 2017 | 5
Arithmetic Queries
?- X is 234556^100.
X = 1058411813164889882981775915184...
?- X is 5/3.
X=1.66666667
?- X is sqrt(3),Y is 3^0.5.
X=Y
Y=1.7320508075688772
?- X is 8 mod 3.
X=2
?- Y is 10^3 * (1+1) + 3.
Y=2003

6. Javier Gonzalez-Sanchez | CSE 240 | Fall 2017 | 6
Question

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Test Yourselves
• X is 5 /3, X = 1.
false
• X is 5 /3; X = 1.
X = 1.6666666667
X = 1
• doSomething(A,B,P) :- P is A + B.
?-doSomething(3,2,P).
?-doSomething(3,2,10).

8. Javier Gonzalez-Sanchez | CSE 240 | Fall 2017 | 8
Recursion
% this is fact
factorial(0, 1).
% this is a rule
% the factorial of F is N*F1
% if N>0 and
% N1 is N-1 and
% the factorial of N1 is F1
factorial(N, F) :-
N>0,
N1 is N - 1,
factorial(N1, F1),
F is N * F1.
?- factorial (3, W).
W=6
1. factorial(3, W)
apply rule 2
2. 3>0, N1 is 3-1, factorial (N1, F1), F is 3 *F1
solve the individual parts
true, 2 is 3-1, factorial (2, F1), F is 3*F1
apply rule 2 again
3. 2>0, N2 is 2-1, factorial (N2, F2), F1 is 2 * F2
solve the individual parts
true, 1 is 2-1, factorial (1, F1), F1 is 2*F2
apply rule 2 again
4. 1>0, N3 is 1-1, factorial (N3, F3), F2 is 2 * F3
solve the individual parts
true, 0 is 1-1, factorial (0, F3), F2 is 1*F3
apply rule 1
5. factorial (0, 1)
F3 is 1
6. Go back, replace F3 to get F2, then F2 to get F1,
then F1 to get F.

9. Javier Gonzalez-Sanchez | CSE 240 | Fall 2017 | 9
Recursion

10. Javier Gonzalez-Sanchez | CSE 240 | Fall 2017 | 10
Test Yourselves
fib(0, 0).
fib(1, 1).
fib(X, Y) :- X > 1,
X2 is X – 2, fib(X2, Y2),
X1 is X – 1, fib(X1, Y1),
Y is Y1 + Y2.

11. Javier Gonzalez-Sanchez | CSE 240 | Fall 2017 | 11
Fibonacci

12. CSE240 – Introduction to Programming Languages
Javier Gonzalez-Sanchez
javiergs@asu.edu
Fall 2017
Disclaimer. These slides can only be used as study material for the class CSE240 at ASU. They cannot be distributed or used for another purpose.

13. Javier Gonzalez-Sanchez | CSE 240 | Fall 2017 | 13
Example 1
Facts
• mother_child(trude, sally).
• father_child(tom, sally).
• father_child(tom, erica).
• father_child(mike, tom).
Rules
• sibling(X, Y) :- parent_child(Z, X), parent_child(Z, Y).
• parent_child(X, Y) :- father_child(X, Y).
• parent_child(X, Y) :- mother_child(X, Y).
Query
• ?- sibling(sally, erica).
Yes