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

4

Answer

33

Answer

10

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

No, comprehensions cannot be nested and cause a compile error

Answer

Only if the inner comprehension uses a numeric range generator

Answer

Only when tabling mode is enabled for the predicate

Question 3

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

Accepted Answer

[4, 6]

Answer

[2, 4, 6]

Answer

[1, 4, 6]

Answer

[2, 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

select(>5, [3,7,2,8,1,6])

Answer

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

Answer

filter([3,7,2,8,1,6], 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 : X in 1..100, X mod 2 =:= 0] computes a running total across iterations

Answer

collect(sum, [X : X in 1..100]) is the standard Picat idiom for summation

Answer

aggregate([X : X in 1..100], sum, even) is the proper form for filtering and summing

Question 6

Which Picat list comprehension generates all pairs (X,Y) where X and Y are both from [1,2,3] and X < Y?

Accepted Answer

[(X,Y) : X in [1,2,3], Y in [1,2,3], X < Y]

Answer

pairs([1,2,3], [1,2,3])

Answer

[X-Y : X,Y in [1,2,3] : X < Y]

Answer

combination([1,2,3], 2)

Question 7

What does sort([X : X in [3,1,4,1,5,9,2,6]]) produce in Picat?

Accepted Answer

[1, 2, 3, 4, 5, 6, 9]

Answer

[1, 1, 2, 3, 4, 5, 6, 9]

Answer

[9, 6, 5, 4, 3, 2, 1]

Answer

[3, 1, 4, 1, 5, 9, 2, 6]