Picat Logic Programming and Unification 5

Question 1

In Picat, what is the difference between `=` and `is` for the expression `X = 2 + 3`?

Accepted Answer

= unifies X with the unevaluated term 2+3; is evaluates it and binds X to 5

Answer

= performs structural unification, so X = 2+3 binds X to the compound term +(2,3), while X is 2+3 evaluates and binds X to 5.

Question 2

When Picat's unification encounters `f(X,X) = f(1,2)`, what is the result?

Accepted Answer

Unification fails because X cannot be both 1 and 2

Answer

Since X appears twice in the pattern, both arguments must unify to the same value; 1 ≠ 2, so unification fails.

Question 3

In Picat logic programming, what does 'resolution' refer to?

Accepted Answer

The inference step that matches a goal with a clause head and produces new subgoals

Answer

Resolution is the core inference step: a goal is matched against a clause head via unification, and the body of that clause becomes new subgoals.

Question 4

Which of the following correctly defines a Picat logic predicate for list membership?

Accepted Answer

member(X,[X|_]).
member(X,[_|T]) :- member(X,T).

Answer

The two-clause recursive definition with a base case (head match) and recursive case (check tail) is the standard logic programming idiom for membership.

Question 5

In Picat, what does the `\=` operator test?

Accepted Answer

That two terms cannot be unified (unification would fail)

Answer

X \= Y succeeds if X and Y cannot be unified; it is equivalent to \+(X = Y) and does not bind variables.

Picat Practice Test

Picat Practice Test

Picat Logic Programming and Unification 5