Re: list iteration for statement

["John Belmonte" <jvb@...>]

ET wrote:
> In C?  C always gets the raw arguments.  And a vararg Lua function
> may still get the 'n' field.  It's not redundant.  Try
>
> print(getn{nil,0,nil})

I see your point there!

A few messages back you corrected my statement about the vm not knowing
about lists, but I should have said the vm doesn't know how to compute n
given an arbitrary table.  That is what had to be added when I implemented
the list-for loop.  As you say the standard library's implementation of getn
is arbitrary, and it may not be a good idea to contaminate the vm with it.

I'm not looking to tackle the list semantics of Lua, I think it's a can of
worms.  With the list-for, I was just trying to make an convenient and fast
equivalent of the foreachi function, which covers at least a third of the
loops I write.

I did a simple timing comparison between the following two loops, in the
case where "n" is already defined, and sum is a local:

        for i = 1, getn(t) do
           sum = sum + t[i]
        end

        for v in t do
            sum = sum + v
        end

The list-for is about 20% faster when t is local, and 30% faster when t is
global.

-John