Picat Pattern Matching Rules 2

Question 1

In Picat, what does the `?=>` operator signify in a rule head compared to `=>`?

Accepted Answer

`?=>` is non-deterministic (allows backtracking); `=>` is deterministic (commits on match)

Answer

Rules using `?=>` are non-deterministic and allow the system to backtrack and try other clauses, while `=>` commits to the first matching clause.

Question 2

Which Picat pattern correctly matches a list with exactly two elements?

Accepted Answer

[X, Y]

Answer

`[X, Y]` matches a list of exactly two elements, binding X to the first and Y to the second.

Question 3

In a Picat rule, a guard expression appears:

Accepted Answer

After the rule head, preceded by a comma, before the neck operator

Answer

A guard is a condition placed after the pattern head and before the `=>` or `?=>` neck, separated by a comma.

Question 4

What happens when no pattern in a Picat function definition matches the given arguments?

Accepted Answer

A runtime exception is thrown

Answer

If no clause pattern matches the arguments, Picat throws an existence error or no-clause exception at runtime.

Question 5

Which pattern in Picat uses an anonymous variable to ignore a list element?

Accepted Answer

[_, X | _]

Answer

The underscore `_` is Picat's anonymous variable that matches any value without binding it.

Picat Practice Test