Solution: Force eager evaluation

Here is a possible solution to the task.

Code

say (1 .. Inf).is-lazy;
say (eager 1..3).is-lazy;
say (lazy 1..3).is-lazy;

🦋 You can find the source code in the file force-eager.raku.

True
False
True

A range up to Inf cannot be computed all at once, so it is lazy: .is-lazy reports True.
The eager prefix forces a list to be produced immediately, so the result is no longer lazy — .is-lazy reports False. This is the direct counterpart of marking a list lazy.
Do not apply eager to an unbounded range: eager 1 .. Inf tries to compute every element at once, so the program simply hangs, consuming more and more memory until it is killed. eager is only safe on lists you know are finite.
The reverse also works: lazy 1..3 marks even a short, finite range as lazy, so .is-lazy reports True. The prefix sets the laziness flag regardless of how small the list is — it does not have to be infinite to be lazy.