Picat Functions vs. Predicates 5

Question 1

In Picat, `map(F, List) = [F(X) : X in List]` defines a higher-order map. Why must `F` be a function reference rather than a predicate reference here?

Accepted Answer

The list comprehension builds its output from return values, requiring `F` to return a value

Answer

Each element `F(X)` must evaluate to a value for inclusion in the new list, so `F` must be a function.

Question 2

What distinguishes a Picat action rule (using `=>`  with an event trigger) from a regular predicate clause?

Accepted Answer

Action rules are triggered by domain events during constraint solving, not by direct calls

Answer

Action rules fire automatically when a variable's domain changes during constraint propagation, unlike regular predicate clauses.

Question 3

Picat's tabling mechanism can be applied to predicates. What is the effect of `table` on a predicate `path/2`?

Accepted Answer

It memoizes computed results to avoid redundant recomputation during search

Answer

The `table` declaration memoizes solutions, enabling efficient dynamic programming over predicates.

Question 4

In Picat, which syntax is used to define a function with multiple return clauses including a default case?

Accepted Answer

Write multiple `= Expr` clauses with pattern matching or guards, ending with a catch-all

Answer

Multiple function clauses with patterns or guards are the idiomatic way to handle multiple cases.

Question 5

Given predicate `between(Lo, Hi, X)` that nondeterministically binds X to each integer in [Lo, Hi], how would you collect all solutions into a list?

Accepted Answer

`findall(X, between(1, 5, X), L)`

Answer

`findall/3` collects all solutions of a goal into a list, bridging nondeterministic predicates and list data.

Picat Practice Test

Picat Practice Test

Picat Functions vs. Predicates 5