On 2009-Sep-20, at 12:48 am, Larry Wall wrote:
Yes, I think it's fair to say that either list context OR a :by turns
a Range into a RangeIterator that matches like a list. Hence, this
ought to match:
(1,3,5) ~~ (1..5 :2by)
OK; but I still have to ask why it returns a RangeIterator instead of
a SeriesIterator or any other plain Iterator. Is there some reason to
make :by work on Ranges that way instead of being, say, an adverb on
"..."? I can see that it's obvious and useful to get a list by
filling in the values between two endpoints, but that also applies to
a pair, or a list of two items.
Having :by effectively work like a list at least reduces the confusion
in the case of numbers, but we're still left with a puzzle when it
comes to strings: Is "b" ~~ "a".."az" false because it's not the case
that a < b < az, or is it true because expanding the list produces a,
b, c, ... ax, ay, az? The former according to spec; but the latter
according to someone who expects a parallel with ints. (Apparently
Rakudo expects that too, at least for the moment.) Of course, in this
case :by doesn't help because there is only one way to increment
strings.
If we give up the Range/RangeIterator duality, we still have the two
different concepts, but I think people will be less tempted to try
making them line up together mentally. (Different things should look
different.) I don't see that we would lose any functionality (make
the :by features work with "..."; or keep ".." and "..." as two ways
to make series, and use infix:<to> for Ranges; or anything else that
distinguishes ranges from iterators). What's the big advantage in
keeping it the way it is?
-David
