Re: [ANN] Lua 5.4.0 (work1) now available

["Soni \"They/Them\" L." <fakedme@...>]

On 2018-03-14 11:11 AM, Roberto Ierusalimschy wrote:
> > I mean: if I can pass something to a function, and I can get it back from a
> > call... well it is a value!
> That is true. But you cannot pass 'undef' to a function or return
> an 'undef' from a function (anymore than you can pass 'while' to a
> function).
>
> -- Roberto

Shouldn't undef just expose the C LUA_TNONE to Lua + some neatness?

With the restrictions that it can only be used as arguments, table 
values, or to undefine locals (non-lexical or semi-lexical variable 
scoping).

string.sub("hello", undef, 3) -- would return "hel"

t[i] = undef -- would erase t[i]

-- non-lexical variable scoping
x = 1
local x = 2
do
  x = undef
  assert(x == 1)
  local x, x, x = 3, 4, 5
  assert(x == 5)
  x = undef
  assert(x == 4)
  x = undef
  assert(x == 3)
  x = undef
  assert(x == 1)
end
assert(x == 2)
-- (this can also be made to work with upvalues obviously. at the end it 
just undefines the global.)

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