Logic Programming and Unification Flashcards

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

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

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

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

Answer: functor/3 and arg/3

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

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

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

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

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

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

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

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

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

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

In Picat, which of the following correctly uses assert to add a fact at runtime?

Answer: assert(likes(mary, food))

assert(Fact) dynamically adds Fact to the knowledge base during program execution.

What is 'goal conjunction' in Picat logic predicates, and how is it written?

Answer: Sequential goal execution where both must succeed, written as G1, G2

Conjunction (G1, G2) means G1 must succeed first, then G2 is attempted; if either fails the conjunction fails.