Picat Pattern Matching Rules 4

Question 1

In Picat, what is the purpose of writing multiple clauses for the same predicate with different patterns?

Accepted Answer

To dispatch behavior based on the structure or value of arguments

Answer

Multiple clauses with different patterns implement structural dispatch — Picat picks the clause whose pattern unifies with the actual arguments.

Question 2

What does `[H|T] = [a, b, c]` produce in Picat?

Accepted Answer

H = a, T = [b, c]

Answer

The unification `[H|T] = [a,b,c]` binds H to the head `a` and T to the tail `[b,c]`.

Question 3

Which of the following is a valid Picat rule that only matches when argument N is positive?

Accepted Answer

positive(N), N > 0 => write(N).

Answer

In Picat rule syntax, the guard `N > 0` is placed after the head pattern and before the `=>` neck, separated by a comma.

Question 4

In Picat, what happens when you use `=` to match a pattern inside a rule body rather than in the head?

Accepted Answer

It performs unification at that point in execution, failing if patterns don't match

Answer

The `=` operator in Picat's body is unification — it tries to make both sides identical and throws an error if it fails.

Question 5

If a Picat function clause has the head `f(0)` and a body, for which calls will this clause be tried?

Accepted Answer

Only calls where the argument unifies with 0

Answer

The literal `0` in the head pattern means the clause is only attempted when the first argument can unify with (equals) 0.

Picat Practice Test