Picat List Comprehensions in Picat

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

{X : X in L, X > 0}

Answer

[X : X in L | X > 0]

Answer

filter(fun(X) => X > 0 end, L)

Question 2

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

Accepted Answer

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

Answer

[X^2 | X <- [1,2,3,4,5]]

Answer

map(X*X, 1..5)

Answer

squares(5)

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

[1, 3, 5]

Answer

[false, true, false, true, false]

Answer

[1, 2, 3, 4, 5]

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

It specifies the output type of the resulting list

Answer

It determines the step size when iterating over a numeric range

Answer

It defines the initial accumulator value for the iteration

Question 5

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

Accepted Answer

[1, 2, 3, 4, 5]

Answer

[0, 1, 2, 3, 4]

Answer

1..5 (an unevaluated range term)

Answer

A lazy sequence that evaluates elements on demand

Question 6

How does Picat handle multiple generators in [X+Y : X in [1,2], Y in [10,20]]?

Accepted Answer

It computes the Cartesian product, yielding [11, 21, 12, 22]

Answer

It computes only the diagonal pairs: (1,10) and (2,20), giving [11, 22]

Answer

It raises an error because multiple generators are not supported

Answer

It interleaves the lists alternately: [11, 12, 21, 22]

Question 7

Which of the following correctly computes the sum of squares of even numbers from 1 to 10 in Picat?

Accepted Answer

sum([X*X : X in 1..10, X mod 2 =:= 0])

Answer

sum_of(X*X, X in 1..10, X mod 2 =:= 0)

Answer

reduce(+, [X*X : X in 1..10, X rem 2 == 0])

Answer

aggregate_sum(X*X, member(X, 1..10), X mod 2 =:= 0)