So further in my thinking of saying BLANK!s are empty? is that we can ask "What is the LENGTH OF a BLANK!"
Trying to shape up the semantics for consistency, I think the LENGTH OF a BLANK! is 0.
BrianH didn't like the idea of R3-Alpha LENGTH? of a NONE being 0. But having split out the roles of nothingness to a finer granularity, we can say:
- LENGTH OF BLANK is 0
- LENGTH OF TRASH is ~error~
- LENGTH OF VOID (antiform) is NULL
- LENGTH OF NULL (antiform) is ~error~
- LENGTH OF NOTHING (antiform) is ~error~
This heeds my policy of saying that if what the routine did would be different e.g. for a string or a block, then blank shouldn't give an answer. But here, both an empty string and an empty block say 0, so I think the length should be 0.
What About REMOVE-EACH and BLANK!
So this is an interesting one, because here you're asking to modify the input in a way that only removes elements from the input...and then returns it and the count.
>> s: [1 2 3 4 5]
>> [series count]: remove-each num s [even? num]
== [1 3 5]
>> series
== [1 3 5]
>> count
== 2
While you can't APPEND to a BLANK! meaningfully, it would be reasonable to argue that you can REMOVE-EACH from a BLANK!...because there are no elements you can remove, and so you can give back the blank and 0.
>> [result count]: remove-each x _ [fail "this part never runs"]
== _
>> result
== _
>> count
== 0
We can do that...but should we?
I'm not sure, but I do feel like this is helping shape the policy on what blanks do. You don't pass blanks into routines and get nulls out when an empty series would not do that. (This is what REMOVE-EACH was doing previously for blank, and I think that was wrong.)