Page 85 - DCAP310_INTRODUCTION_TO_ARTIFICIAL_INTELLIGENCE_AND_EXPERT_SYSTEMS

Unit 5: Artificial Intelligence Programming Language

Notes
Example 2: Consider the following fact.

p([H|T], H, T).
Lets see what happens when we ask some simple queries.
?- p([a,b,c], X, Y).
X=a
Y=[b,c]

yes
?- p([a], X, Y).
X=a

Y=[ ]
yes
?- p([], X, Y).
no

5.6.2 Prolog Sequences

The kind of sequences most used in Prolog is “comma” sequences. There is no empty sequence
(unlike for lists). The shortest sequence has one element. Longer sequences have elements
separated by commas “,”. An appropriate declaration for the comma operator would be

:- op(1000,xfy,’,’).
meaning that comma is right-associative with precedence 1000. (The comma operator is actually
built-in.) Here is some Prolog behavior.
?- (H,T) = (1,2,3,4).
H = 1
T = 2,3,4
?- (a) = a.
Yes
?- (H,T) = (a).
No
?- (A,B,C) = (1,2,3,4,5).
A = 1
B = 2
C = 3,4,5
Prolog clauses use comma sequences.
?- assert((a(X):- b(X),c(X),d(X))). %% Note parens around clause
X = G1056
?- clause(a(X),Body), Body=(First,Next).
First = b(G1176)
Next = c(G1176), d(G1176)
Body = b(G1176), c(G1176), d(G1176)
X = G1176
Processing sequences is similar to processing lists, except that the base case for sequences is a
unit sequence (one element), whereas for lists the base case is for the empty list.

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