Re: new "empty" value/type in Lua?

[Coda Highland <chighland@...>]

>From a CS perspective, all computable algorithms can be expressed by a
Turing machine. That doesn't mean there aren't comparative merits
between them.

/s/ Adam

On Mon, Jul 1, 2013 at 12:35 PM, Tim Hill <drtimhill@gmail.com> wrote:
> I would say that from a CS perspective, table.has() and an "empty" sentinel are the same thing in different form; both introduce an extra bit of information about an element in the table, since you now have two possibilities when faced with t[k] = nil: one with table.has() true, one with table.has() false. Logically you could define:
>
> function empty(t, k) return t[k] == nil and table.has(t,k) end
>
> --Tim
>
> On Jul 1, 2013, at 12:13 PM, Coda Highland <chighland@gmail.com> wrote:
>
>> On Mon, Jul 1, 2013 at 12:11 PM, Tim Hill <drtimhill@gmail.com> wrote:
>>>>> That could be useful, but also a bit confusing as it means a key set to nil
>>>>> and a key that was never set (or was deleted) are different things, but both
>>>>> have a nil value.
>>>> You can tell the difference with table.has().
>>> Depending on how # behaved, you might also be able to tell with just (i <=
>>> #t) ?
>>
>> table.has() is a generic mechanism for all tables, not just arrays --
>> a sparse array or a freeform table could still have nil-valued entries
>> as distinct from nonexistent entries.
>>
>> /s/ Adam
>>
>
>