Picat Functions vs. Predicates 4

Question 1

What does Picat's `to_string/1` function do that a predicate could not directly accomplish?

Accepted Answer

It returns a string value usable inline in expressions like `print(to_string(42) ++ "!")`

Answer

As a function, `to_string/1` returns a value immediately composable with operators like `++`.

Question 2

In Picat, which of the following correctly adds a guard to a predicate clause?

Accepted Answer

classify(X), X > 0 => println(positive)

Answer

In Picat, a guard is placed between the head and the `=>` neck using a comma: `Head, Guard => Body`.

Question 3

Picat functions can be higher-order. Which call correctly applies function `F` to value `X` and uses the result?

Accepted Answer

Result = call(F, X)

Answer

In Picat, `call(F, X)` invokes a function reference `F` with argument `X` and returns the result.

Question 4

What is the key reason you cannot use a predicate directly inside a list comprehension expression in Picat?

Accepted Answer

List comprehensions expect expressions that yield values, which only functions provide

Answer

List comprehension expressions like `[f(X) : X in L]` require `f` to return a value, so `f` must be a function.

Question 5

A Picat module exports both `area/1` (function) and `print_area/1` (predicate). Which import style correctly handles both?

Accepted Answer

import geometry

Answer

`import ModuleName` imports all exported functions and predicates from the module.

Picat Practice Test