That make unuseful the = operation, because it is not = of sets... If zilde is different of B with operation ≡ it is wrong and unuseful that symbol too ... The = for sets in math is defined as W=B <=> (Ax xeW=>xeB)/(Ax xeB=>xeW)
Void set has not a type (or all the types), it is a list and a set too I would say
@RosLuP an apl array is not just content. it's more like a triple of (type; shape; content), and the order of elements everywhere is significant
the reason we have = and ≡ as separate functions is that = is often useful as an arithmetic operation, penetrating to the scalars just like +, ×, etc do
we call ≡ "match" instead of "equal". it compares all three components - type, shape, and content.
in the case of empty arrays, we consider content to consist of a single prototypical element - those are also taken into consideration by ≡
@RosLuP i agree, it would be simpler and therefore better to be able to say just "this is a void list"
(though i've never had any objections against typed empty results from my golfing programs)
but consider also the opposite - what if your input is empty without any information about type, shape, or prototypical content?
task: given a list of debit-credit pairs, check if the books are balanced, i.e. report whether the sum of debits equals the sum of credits
even for a simple task like ^this you wouldn't be able to write the obvious solution =/⊃+/⎕ because it requires a special case for empty input
another example: surround a string with spaces, {¯1⌽⍵↑⍨2+⍴⍵}. if '' is indistinguishable from ⍬, you might get 0 0 instead of ' ' when the input is void
@ngn if this function would be something as ∧/{=/⍵}¨(1 1)(3 3) than ∧/{=/⍵}¨ /voidlist is one error in every type of voidlist or for me it has return 1 for voidlist for each type
For the second function I not would write it for what I know because ⍵↑/voidset it should be voidset . So ⍵↑zilde for me it is not zilde omega times but just zilde (because it is not so I will not use that)
@RosLuP then this is just opinion. I think 10↑'' being spaces can be useful (and I definitely think it shouldn't just return ⍬ in any case), you may not.
