unset! transparency in any and all

[Oldes]

Should I make this change?
Current version (compatible with Red (almost) and Rebol2):

any []     ;== none
any [()]   ;== #[unset!]
any [() 1] ;== #[unset!]
all [1 ()] ;== #[unset!]
all []     ;== true (in Red none)
all [()]   ;== #[unset!]

after change:

any []     ;== none
any [()]   ;== none
any [() 1] ;== 1
all [1 ()] ;== 1
all []     ;== true
all [()]   ;== true

In original R3 alpha it was:

any []     ;== none
any [()]   ;== none
any [() 1] ;== 1
all [1 ()] ;== #[unset!]
all []     ;== true
all [()]   ;== #[unset!]

Related discussion: http://www.rebol.net/cgi-bin/r3blog.r?view=0207
Related issues:
Oldes/Rebol-issues#564
Oldes/Rebol-issues#850
Oldes/Rebol-issues#2248
And also:
red/REP#85
red/red#4469
red/red#4482

[acook]

Reading into the old issues is pretty interesting. To me it is surprising that unset wouldn't be treated like none, but the argument is compelling to ignore them entirely. So I'm okay with either approach.

[Oldes]

This is better:

unset? all []     ;== true
unset? all [()]   ;== true

[Oldes]

So now it is:

all [
  print "Testing ANY"
   none? any []
   none? any [()]
     1 = any [() 1]

  print "Testing ALL"
     1 = all [1 ()]
  unset? all []
  unset? all [()]

  print "Tests OK"
] ;== true

[hostilefork]

For whatever it is worth 🤷 I have decided that my analogue to "unset!" should be truthy. So Ren-C's handling in ANY and ALL matches Red's... where they, uh, sort of treat it as true:

red>> if get/any 'asdf [print "truthy"]
truthy

red>> either get/any 'asdf [print "truthy"] [print "falsey"]
*** Script Error: block did not return a value  ; <-- huh?

red>> unset? all [get/any 'asdf]
== true

red>> unset? any [get/any 'asdf]
== true

red>> case [get/any 'asdf [print "truthy"]]
*** Script Error: block did not return a value  ; <-- huh, again?

I provide my rationale for why truthiness is the right answer here (note I call the unset state "nothing", because I believe variables are unset not values. e.g. UNSET? 'VAR.)

https://forum.rebol.info/t/the-truthiness-of-nothing/2180

Also I give some rationale for why I think Rebol2 was correct to not allow UNSET! in comparison operators.

(I'll mention that in Ren-C, () does not produce NOTHING...but rather, a VOID. So your particular example above would have the opt out behavior you show.)

It would be some kind of freakish miracle if all of us could agree to make it truthy, allowed to assign a SET-WORD! without error, and not accepted by comparison operators. 😛