Martin Kay

1
Introduction to
Prolog

• Martin Kay
• Stanford University

2
Topics

• Books
• Starting and stopping Prolog
• Consulting and reconsulting files
• Assertions and queries
• Constants and variables
• Nondeterminism
• Lists
• Facts and rules

3
Books

• Bratko, I. (1986) Prolog Programming for
  Artificial Intelligence. International Computer
  Science Series, Addison Wesley.
• Clocksin, W. F. and C. S. Mellish (1981)
  Programming in Prolog. Springer-Verlag, Berlin.
• König, E. and R. Seiffert (1989) Grudkurs Prolog
  für Linguisten. UTB für Wissenschaft
  Uni-Taschenbücher, A. Franke Verlag, Tübingen.
• O'Keefe, R. (1990) The Craft of Prolog. MIT
  Press, Cambridge, Massachusetts.
• Ross, P. (1989) Advanced Prolog. Addison Weseley.
• Sterling, L. and E. Shapiro (1986) The Art of
  Prolog. MIT Press, Cambridge, Massachusetts.

4
Sicstus Prolog

• Swedish Institute of Computer Science (SICS)

Setting the path environment variable (on Leland)
elaine27gt more .cshrc _at_() Leland Systems
.cshrc version 3.0.4 elaine27gt more .cshrc
_at_() Leland Systems .cshrc version
3.0.4 .... set path( /afs/ir/class/ling138/b
in path) ....
5
Sicstus Prolog

• Swedish Institute of Computer Science (SICS)

1 sicstus SICStus 2.1 9 Fri Oct 21 163141
PDT 1994 ?- halt. 2
6
(No Transcript)
7
(No Transcript)
8
(No Transcript)
9
(No Transcript)
10
Queries
11
Queries
Now we can make this a real link!
12
(No Transcript)
13
Consulting files

• ?- consult(maize).
• consulting /tmp_mnt/tilde/kay/pl/parsers/maize.pl
  ...
• /tmp_mnt/tilde/kay/pl/parsers/maize.pl
  consulted, 160 msec 1056 bytes
• yes
• ?-

consult(maize.pl). maize. maize.pl.
14
Facts and Rules

• past(dive, dived).
• past_tense(dive, dove).
• pres_part(dive, diving).
• sing3(dive, dives).
• past_tense(write, wrote).
• past_part(write, written).
• pres_part(write, writing).
• sing3(write, writes).
• past_part(Verb, Word) -
• past(Verb, Word).
• past_tense(Verb, Word) -
• past(Verb, Word).

Head
Goal
15
The /2 operator

• ?- Xfoo.
• X foo ?
• yes
• ?- XY.
• Y X ?
• yes
• ?- foo(A, b)foo(a, B).
• A a,
• B b ?
• yes

16
Unification

• ?- p(a, Q, b) p(A, A, A).
• no
• ?- p(a, Q, R) p(A, A, A).
• A a,
• Q a,
• R a
• yes
• ?- p(q(a, a), r(X, X), s(Y, Y))p(X, Y, Z).
• X q(a,a),
• Y r(q(a,a),q(a,a)),
• Z s(r(q(a,a),q(a,a)),r(q(a,a),q(a,a))) ?
• yes

17
Ordered Pairs
?- Xa b c . Xa, b, c yes
?- Xa b. Xa b yes
18
member/2

• ?- member(b, a,b,c).
• yes
• ?- member(X, a, b, c).
• X a ?
• X b ?
• X c ?
• no
• ?- member(a, X, b, Y).
• X a ?
• Y a ?
• no

member(H, H_). member(X, _T) -
member(X, T).
19
append/3

• ?- append(a, b, c, p, q, r, X).
• X a,b,c,p,q,r ?
• yes
• ?- append(a, b, c, X, a, b, c, d, e, f).
• X d,e,f ?
• yes
• ?- append(X, d, e, f,a, b, c, d, e, f).
• X a,b,c ?
• yes

append(, A, A). append(CD, A, CB) -
append(D, A, B).
20
(Naive) reverse/2

• ?- reverse(a, b, c, X).
• X c,b,a ?
• yes
• ?- reverse(X, a, b, c).
• X c,b,a ?
• yes
• ?- Xa, b, B, A, reverse(X, X).
• A a,
• B b,
• X a,b,b,a ?
• yes

reverse(, ). reverse(HT, Rev) -
reverse(T, RT), append(RT, H, Rev).
21
Interrupting Prolog

• foo(a, b).
• C
• Prolog interruption (h for help)? a
• Execution aborted
• ?-