Picat General 4

Question 1

What is a 'guard' in a Picat rule, and where does it appear?

Accepted Answer

A boolean condition placed between the head and => that must hold for the rule to fire

Answer

A guard is an optional boolean test in the rule head, written before `=>`, that refines when a particular clause applies.

Question 2

Which Picat predicate retrieves all solutions of a goal as a list?

Accepted Answer

findall(Template, Goal, List)

Answer

`findall/3` collects every Template instantiation for which Goal succeeds into List, returning [] if Goal always fails.

Question 3

In Picat, what does the `@` symbol signify when used in a term like `[H|T]@List`?

Accepted Answer

It aliases the whole list to List while also destructuring

Answer

Picat supports as-patterns with `@`, so `[H|T]@List` matches a non-empty list, binding H to the head, T to the tail, and List to the entire structure simultaneously.

Question 4

What distinguishes a Picat `function` (using = in the head) from a `predicate`?

Accepted Answer

A function must return exactly one value via the last argument position, while a predicate succeeds or fails

Answer

In Picat, a function definition uses `f(Args) = Value => Body`, returning a deterministic value, whereas a predicate succeeds or fails without an explicit return.

Question 5

Which constraint in Picat's `cp` module ensures all variables in a list take distinct values?

Accepted Answer

all_different(Vars)

Answer

`all_different/1` posts a global constraint requiring every variable in the list to be assigned a different value.

Picat Practice Test

Picat Practice Test

Picat General 4