Introduction to Prolog 20070524 Prolog 1 History of Prolog - PDF document

Introduction to Prolog 20070524 Prolog 1 History of Prolog PROgramming in LOGic • - based on logic - a popular artificial intelligence language - Horn subset of first-order Predicate Logic Developed by • Robert A. Kowalski (Univ. of Edinburgh) and Alain Colmerauer (Univ. of Aix-Marseille) in early of 1970 First Prolog Interpreter by Colmerauer • First Prolog Compiler by David Warren • (Univ. of Edinburgh) 20070524 Prolog 2 1

Some Available Prolog Systems SWI-Prolog 5.6.34 (2007 released) • http://www.swi-prolog.org/ SWI-Prolog-Editor 3.03 • http://lernen.bildung.hessen.de/informatik/swiprolog/indexe.htm Visual Prolog 7.0 (March 26, 2007 released) • http://www.visual-prolog.com/ Successor of Turbo Prolog (by Borland) SICStus Prolog 4.0.1 (May 17, 2007 released) • http://www.sics.se/isl/sicstuswww/site/index.html GNU GProlog 1.3.0 • http://www.gprolog.org/ …… • 20070524 Prolog 3 Screenshot 20070524 Prolog 4 2

Some Basic Concepts Prolog character set • - Uppercase letters, A-Z - Lowercase letters, a-z - Digits, 0-9 - Symbols, + - * / \ ^ , . ~ : . ? @ # $ & Term • - a single data structure as the foundation of the language - can be integer, atom (beginning with a lowercase, or quoted by ‘), variable (beginning with a uppercase), structure (complex term, functor(arg1, arg2)) e.g. may date(Day, june, 2002) 20070524 Prolog 5 Some Basic Concepts (cont.-1) A prolog program (.pl) • - consists of a sequence of clauses A clause is either • - fact predicate(arg1, arg2, … argN). - rule head :- body. - query (or goal) 20070524 Prolog 6 3

Some Basic Concepts (cont.-2) Query • - If there is a fact that matches the goal, then the query succeeds and responds 'yes’ otherwise the query fails and responds with 'no.‘ room(kitchen). room('dinning room'). room(cellar). ?- room( kitchen ). Yes ?- room( teacher ). No ?- room( X ). X=kitchen ; X=‘dinning room’ ; X=cellar ; No ‘No' means there are no more answers 20070524 Prolog 7 Some Basic Concepts (cont.-3) 先點選執行 C:\Program Files\pl\bin\plwin.exe 按 File/Consult 選桌面 /prologrun/room.pl 20070524 Prolog 8 4

Some Basic Concepts (cont.-4) [yyy] or [‘yyy’] 表示 File/Consult 選桌面 /prologrun/yyy.pl 20070524 Prolog 9 Some Basic Concepts (cont.-5) [swi(‘xxx/yyy’)] 表示 File/Consult 選 C:/program files/pl/xxx/yyy.pl 20070524 Prolog 10 5

Some Basic Concepts (cont.-6) location(apple, kitchen). edible(apple). location(crackers, kitchen). edible(banana). location(boiler, kitchen). edible(crackers). location(banana, classroom). ?- location(X, kitchen), edible(X). X = apple ; X = crackers ; No 20070524 Prolog 11 Some Basic Concepts (cont.-7) List • - a collection of terms - denoted by square brackets with the terms separated by commas - or denoted by [X | Y] X is the first element of the list, called the head. Y is the list of remaining elements, called the tail. e.g. [a, b, c] [a | [ b, c ] ] [a | [ b | [ c ] ] ] 5 different representations [a | [ b | [ c | [ ] ] ] ] [a, b | [c ] ] 20070524 Prolog 12 6

Some Basic Concepts (cont.- 8 ) 'car' refers to the first element of a list, 'cdr ' refers to the tail or rest of the list, and 'cons' is the list constructor. car([X|Y],X). cdr([X|Y],Y). cons(X,R,[X|R]). 20070524 Prolog 13 Some Basic Concepts (cont.-9) member(X,[X|R]). % X is a member of a list whose first element is X. member(X,[Y|R]) :- member(X,R). % X is a member of a list % whose tail is R if X is a member of R. ?- member(2,[1,2,3]). Yes ?- member(X,[1,2,3]). X = 1 ; X = 2 ; X = 3 ; No 20070524 Prolog 14 7

A Good Prolog Tutorial http://www.intranet.csupomona.edu/~jrfisher/www/ prolog_tutorial/pt_framer.html 20070524 Prolog 15 Prolog Example 1 The facts about the Dutch Royal Family %?- parent(beat,alex). %?- parent(beat,X). %?- parent(jul,X). mother(wil,jul). mother(jul,beat). mother(jul,chris). mother(beat,friso). father(hend,jul). father(bern,beat). father(bern,chris). father(claus,friso). parent(X, Y) :- mother(X,Y). parent(X, Y) :- father(X,Y). 20070524 Prolog 16 8

Prolog Example 1 (cont.) 20070524 Prolog 17 Prolog Example 2 % sum(L,N) which succeeds where N is the sum of the integers % in the list L. (Assume that list L will be given, % and that this list contains only integers). % % ?- sum([1,2,3,4], N). sum([],0). sum([H|T],N) :- sum(T,N1), N is N1 + H. 20070524 Prolog 18 9

Prolog Example 2 (cont.) 20070524 Prolog 19 Prolog Example 3 nat(0). nat(N) :- nat(M), N is M + 1. ?- nat(N), write(N), nl, fail. 0 1 % Successive numbers are generated 2 % by backtracking 3 4 …. 20070524 Prolog 20 10

Prolog Example 4 % Hanoi tower % ?- move(3,left,right,center). move(1,X,Y,_) :- write('Move top disk from '), write(X), write(' to '), write(Y), nl. move(N,X,Y,Z) :- N>1, M is N-1, move(M,X,Z,Y), move(1,X,Y,_), move(M,Z,Y,X). 20070524 Prolog 21 Prolog Example 4 (cont.) 20070524 Prolog 22 11

Prolog Example 5 factorial(0,1). factorial(N,F) :- N>0, N1 is N-1, factorial(N1,F1), F is N * F1. ?- factorial(3,W). W=6 Yes ?- factorial(3,6). Yes ?- factorial(5,2). No 20070524 Prolog 23 Prolog Example 5 (cont.-1) 20070524 Prolog 24 12

Prolog Example 5 (cont.-2) http://www.csupomona.edu/~jrfisher/www/prolog_tutorial/2_2.html 20070524 Prolog 25 Map Coloring 20070524 Prolog 26 13

Map Coloring (cont.-1) adjacent(1,2). adjacent(2,1). adjacent(1,3). adjacent(3,1). adjacent(1,4). adjacent(4,1). adjacent(1,5). adjacent(5,1). adjacent(2,3). adjacent(3,2). adjacent(2,4). adjacent(4,2). adjacent(3,4). adjacent(4,3). adjacent(4,5). adjacent(5,4). ?- adjacent(2,3). Yes ?- adjacent(5,3). No ?- adjacent(3,R). R = 1 ; R = 2 ; R = 4 ; No 20070524 Prolog 27 Map Coloring (cont.-2) conflict(R1,R2,Coloring) :- adjacent(R1,R2), color(R1,Color,Coloring), color(R2,Color,Coloring). ?- conflict(R1,R2,b). R1 = 2 R2 = 4 Yes ?- conflict(R1,R2,b),color(R1,C,b). R1 = 2 R2 = 4 C = blue Yes 20070524 Prolog 28 14

Who owns the zebra There are five houses. Each house has it's own unique color. All homeowners are of different nationalities. They all have different pets. They all drink different drinks. They all smoke different cigarettes. The Englishman lives in the red House. The Swede has a dog. The Dane drinks Tea. The green house is on the left side of the white house. In the green house they drink coffee. The man who smokes Pall Mall has birds. In the yellow house they smoke Dunhill. In the middle house they drink milk. The Norwegian lives in the First house. The man who smokes Blend lives next door to the house with cats. In the house next to the house with a horse, they smoke Dunhill. The man who smokes Blue Master drinks beer. The German smokes Prince. The Norwegian lives next to the blue house. They drink water in the house next to where they smoke Blend. Who owns the Zebra? 20070524 Prolog 29 Who owns the zebra (cont.-1) next_to(X, Y, List) :- is_right(X, Y, List). next_to(X, Y, List) :- is_right(Y, X, List). is_right(R, L, [L | [R | _]]). is_right(R, L, [_ | Rest]) :- is_right(R, L, Rest). house(C, N, P, D, S) predicate • C: the color of the house N: the nationality of the resident P: the resident's pet D: the resident's drink S: the resident's cigarette There are five houses • Street = [_House1, _House2, _House3, _House4, _House5], The Englishman lives in the red House. • member(house(red, englishman, _, _, _), Street), 20070524 Prolog 30 15

Who owns the zebra (cont.-2) ?- owns_zebra(Street, Who). Street = [house(yellow, norwegian, fox, _G473, kools), house(blue, ukrainian, horse, tea, chesterfields), house(red, englishman, snails, milk, old_gold), house(ivory, spaniard, dog, orange_juice, lucky_strike), house(green, japanese, zebra, coffee, parliaments)] Who = japanese Yes 20070524 Prolog 31 16