Picat Logic Programming and Unification 3

Question 1

In Picat, how does the `=>` rule differ from a logic predicate clause written with `:-`?

Accepted Answer

=> commits to the first matching rule (no backtracking into it); :- allows backtracking

Answer

A => (deterministic) rule commits once matched — no alternative clauses are tried on failure — while :- clauses participate in full backtracking.

Question 2

Which Picat built-in decomposes a compound term into its functor and arguments?

Accepted Answer

functor/3 and arg/3

Answer

functor(T, F, A) extracts functor F and arity A, while arg(N, T, Arg) extracts the Nth argument of T.

Question 3

What does the Picat goal `T =.. [foo, 1, 2]` do?

Accepted Answer

Unifies T with the compound term foo(1,2)

Answer

The univ operator =.. constructs or decomposes a term: [foo,1,2] as the right-hand side builds foo(1,2).

Question 4

In Picat logic predicates, what is the purpose of `call/1` or `call/N`?

Accepted Answer

Calls a goal stored in a variable at runtime (meta-call)

Answer

call/N allows a term held in a variable to be invoked as a goal, enabling higher-order programming.

Question 5

What does the `once/1` built-in do in Picat?

Accepted Answer

Runs a goal and commits to its first solution, discarding other choice points

Answer

once(Goal) succeeds at most once: it runs Goal and keeps only the first solution, cutting away alternatives.

Picat Practice Test