1. List Manipulation in Prolog
A Non-list Example
Prolog's List notation
List manipulation techniques
Append
Running definitions forwards and backwards
CSE S. Tanimoto Lists in Prolog

2. CSE 341 -- S. Tanimoto Lists in Prolog
Example
% courses.pl Some prerequisite relationships
prereq(cse142, cse143).
prereq(cse143, cse341).
prereq(cse341, cse473).
before(X, Y) :- prereq(X, Y).
before(X, Y) :- prereq(X, Z), before(Z, Y).
CSE S. Tanimoto Lists in Prolog

3. CSE 341 -- S. Tanimoto Lists in Prolog
A Session
?- consult(courses).
% courses compiled 0.00 sec, 1,088 bytes
Yes
?- prereq(cse142, cse143).
?- prereq(cse142, X).
X = cse143 ; No
CSE S. Tanimoto Lists in Prolog

4. CSE 341 -- S. Tanimoto Lists in Prolog
A session (cont)
?- prereq(X, Y).
X = cse142
Y = cse143 ;
X = cse143
Y = cse341 ;
X = cse341
Y = cse473 ; No ?-
CSE S. Tanimoto Lists in Prolog

5. CSE 341 -- S. Tanimoto Lists in Prolog
A session (cont)
?- before(X, cse341).
X = cse143 ;
X = cse142 ; No
CSE S. Tanimoto Lists in Prolog

6. CSE 341 -- S. Tanimoto Lists in Prolog
colors([r, g, b]).
?- colors(L).
L = [r, g, b]
?- colors([X|Y]).
X = r, Y = [g, b]
% X is the head. Y is the tail.
?- mylist([a, [b, c]]).
CSE S. Tanimoto Lists in Prolog

7. Defining Predicates on Lists
car([X|L], X).
cdr([X|L], L).
cons(X, L, [X|L]).
?- car([a, b, c], X).
X = a
?- cdr([a, b, c], X).
X = [b, c]
?- cons(a, [b, c], X).
X = [a, b, c]
CSE S. Tanimoto Lists in Prolog

8. CSE 341 -- S. Tanimoto Lists in Prolog
concat a.k.a. append
concat([], L, L).
concat([X|L1], L2, [X|L3]) :- concat(L1, L2, L3).
?- concat([a, b, c], [d, e], X).
X = [a, b, c, d, e]
?- concat(X, [d, e], [a, b, c, d, e]).
X = [a, b, c]
CSE S. Tanimoto Lists in Prolog

9. CSE 341 -- S. Tanimoto Lists in Prolog
concat used backwards
?- concat(X, Y, [x, y, z]).
X = []
Y = [x, y, z] ;
X = [x]
Y = [y, z] ;
X = [x, y]
Y = [z] ;
X = [x, y, z]
Y = [] ; No
CSE S. Tanimoto Lists in Prolog

10. Logic Prog. vs Functional Prog.
Functional programming: evaluation is one-way.
Logic programming: evaluation can be two-way.
CSE S. Tanimoto Lists in Prolog