Picat List Comprehensions in Picat 2

Question 1

What is the length of the list produced by [X : X in 1..10, X mod 3 =:= 0] in Picat?

Accepted Answer

3

Answer

Multiples of 3 from 1 to 10 are 3, 6, and 9 — exactly 3 values — so len([X : X in 1..10, X mod 3 =:= 0]) equals 3.

Question 2

Can the result of a Picat list comprehension be used as the source list in another comprehension?

Accepted Answer

Yes, a comprehension evaluates to a plain list and can serve as the generator in an outer comprehension

Answer

A Picat list comprehension evaluates eagerly to an ordinary list, so it can appear wherever a list is expected, including as the generator source in another comprehension.

Question 3

What does [X*2 : X in [1,2,3], X > 1] produce in Picat?

Accepted Answer

[4, 6]

Answer

The condition X > 1 excludes X=1, so only X=2 (producing 4) and X=3 (producing 6) pass the filter, giving [4, 6].

Question 4

Which Picat expression filters the list [3,7,2,8,1,6] to keep only elements greater than 5?

Accepted Answer

[X : X in [3,7,2,8,1,6], X > 5]

Answer

The list comprehension [X : X in [3,7,2,8,1,6], X > 5] iterates the list and retains only 7, 8, and 6, which satisfy X > 5.

Question 5

Which of the following demonstrates using a Picat list comprehension with a built-in aggregate operation?

Accepted Answer

sum([X : X in 1..100, X mod 2 =:= 0]) computes the sum of all even numbers from 1 to 100

Answer

sum/1 accepts any list, so sum([X : X in 1..100, X mod 2 =:= 0]) builds the list of even numbers then sums them, equaling 2550.

Picat Practice Test

Picat Practice Test

Picat List Comprehensions in Picat 2