Re: NaN (was: Re: The Undefined Country (was Re: Quest: real world "Lua array with holes" usage))

[Egor Skriptunoff <egor.skriptunoff@...>]

On Mon, Jul 25, 2016 at 2:02 PM, steve donovan <steve.j.donovan@gmail.com> wrote:

> The "holes problem" exists only in the context of sequences,
> so introducing "null" type is not a good idea as it affects the whole
> language.

It would not be a type - it would be equivalent to you having declared
'null = {}'. It becomes a convention that module writers can depend
on.

What would ({})[1] be equal to: null or nil?

BTW, "null" may be a function which can be used to check for equality to itself:

-- Definition

local function _NIL (value) return value == _NIL or value == nil end

_G._NIL = _NIL

-- Usage

if not _NIL(v) then ... end

 

> local tbl, idx_from, idx_to = table.pack(...)

Hm, then why not `local tbl, n = table.pack(...)?

 

1) For symmetry:
table.unpack(table.pack()) should be an identity

2) For storing sequence in a single value (to make array of sequences, for example):

-- tuple to single value

local v = {table.pack(...)}

-- tuple from single value :-)

forward(table.unpack(table.unpack(v)))