Picat List Comprehensions in Picat 1

Question 1

What is the correct Picat syntax for a list comprehension that collects all elements X from list L where X > 0?

Accepted Answer

[X : X in L, X > 0]

Answer

Picat list comprehensions use the form [Expr : Var in List, Condition], where conditions after the comma act as filters on the generated elements.

Question 2

Which Picat expression generates the list [1, 4, 9, 16, 25]?

Accepted Answer

[X*X : X in 1..5]

Answer

In Picat, [X*X : X in 1..5] uses a range generator to iterate X from 1 to 5 inclusive and computes X*X for each value, yielding [1,4,9,16,25].

Question 3

What does [X : X in [1,2,3,4,5], X mod 2 =:= 0] evaluate to in Picat?

Accepted Answer

[2, 4]

Answer

The condition X mod 2 =:= 0 selects only even numbers; from [1,2,3,4,5] only 2 and 4 are even, so the result is [2, 4].

Question 4

In a Picat list comprehension [Expr : Var in Generator, Condition], what role does the Condition play?

Accepted Answer

It is a goal that must succeed for the current element to be included in the result

Answer

The condition is a goal (a predicate call or comparison) that must succeed for each candidate element; only elements for which it holds are included in the output list.

Question 5

What is the output of [X : X in 1..5] in Picat?

Accepted Answer

[1, 2, 3, 4, 5]

Answer

The range 1..5 in a Picat list comprehension generates integers 1 through 5 inclusive, so [X : X in 1..5] produces the fully evaluated list [1,2,3,4,5].

Picat Practice Test

Picat Practice Test

Picat List Comprehensions in Picat 1