Picat Logic Programming and Unification 4

Question 1

In Picat, what is a 'choice point' in the context of logic programming?

Accepted Answer

A saved execution state that Picat can return to on backtracking

Answer

A choice point is a snapshot of the interpreter state saved when multiple clauses can match, allowing resumption on failure.

Question 2

How does Picat's cut (`!`) affect choice points in a logic predicate?

Accepted Answer

Removes all choice points created since the parent call, committing to the current clause

Answer

Cut removes all choice points for the predicate that contains it, preventing backtracking into alternative clauses.

Question 3

In Picat unification, which of the following is a valid unification of a list?

Accepted Answer

[H|T] = [1,2,3] → H=1, T=[2,3]

Answer

List unification [H|T] = [1,2,3] binds the head H to 1 and the tail T to the remaining list [2,3].

Question 4

What does `findall(X, member(X,[1,2,3]), Bag)` return in Picat?

Accepted Answer

Bag = [1,2,3]

Answer

findall/3 collects all X that satisfy the goal into Bag, so Bag = [1,2,3].

Question 5

In Picat, what distinguishes `bagof/3` from `findall/3`?

Accepted Answer

bagof groups results by unbound variables and fails if there are no solutions; findall never fails

Answer

bagof/3 fails when the goal has no solutions and can group answers by free variables, unlike findall/3 which always succeeds with [] on no solutions.

Picat Practice Test