Re: another hat in the ring regarding Lua 5.2: static typing

[Tomas Guisasola Gorham <tomas@...>]

On Fri, 29 Feb 2008, steve donovan wrote:
> On Thu, Feb 28, 2008 at 9:16 PM, Asko Kauppi <askok@dnainternet.net> wrote:
> >         local function mydear( t :string_or_table, i :int, j :[int], n :
> >  [number] )
> >             : string, table, [int]
> >                 ...function body with returns...
> >         end
> 
> Nice notation!  I was thinking about this general problem the other
> day: how does one explcitly specify type in a dynamic language? The
> idea was that types are objects, and one builds them up with
> expressions:
>     string_or_table = choice(String,Table)
>     string_or_nil = choice(String,Nil)
>     Location = choice({X=Double,Y=Double},{Double,Double})
	I like that syntax either, but I have some doubts :-)
	Could you accept a proxy table instead of the real table?
How would you specify that?  How would you specify properties of
objects?  An example of what I am looking for is:

function get_status (db, id)
	local cond = "id="..id.." AND estado_retorno is not null"
	return db:select ("status", "processo", cond)()
end

	How would you specify that you can call db's select?
I am not interested in the real type of db: it could be a userdata
or a table, and in this case it could have the field select or it
could have a metatable with a __index metamethod; also, the select
object could be a function or a "callable" object...  How would you
manage that?
	I am not sure if we should check the _type_ or the operations
we want.  In my case, I only care about db.select being a callable
object.  One might argue that I would have to check its arguments,
but I would delegate it for the call itself.

	Regards,
		Tomas