List comprehension is a bad idea, IMO. They were an improvement over not having anything like it, but python has improved over it (https://wiki.python.org/moin/Generators)

⇒ Generator expressions are the way to go. They would give you the sequence of elements without generating the (potentially enormous) data structure.

From there, methods to reify the items in a sequence would give you your list, array, or dictionary, where needed.

So, for Swift, I wouldn’t use

    Array(1..<5, 3..<5) { ($0, $1) }

but the slightly longer

    Array(for i in 1..<5, j in 3..<5 yield (i,j))

I’m not sure that is easy to fit in the existing parser, though. If it can be fit in, I would allow that code in ‘normal’ nested for loops, too.