E03: Laziness: The Catch

So, jnthn++ fixed the Nominal type check failed for parameter '@a'; expected Positional but got GatherIterator instead issue. Errr, sort of. Here's my sum sub:


sub sum(@a) {
+@a ?? @a.reduce({ $^a + $^b }) !! 0;
}


Now it does get called properly if you say sum(@costs.grep({$_ >= 1000})). But even though it appears to be a very simple function, it doesn't work when called this way! The problem, as far as I can tell, is that @a may look like a Seq or an Array, it's still actually an iterator. That means the first time you use it for something like, say, +@a, it is completely consumed! Then the next time you access it, there's nothing left. This is definitely not what is expected...

Update: Just realized that without "Perl 6", Ironman didn't pick up the previous post or this one. Time to edit...