Re: Making LUA safe to execute untrusted scripts [replay]
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- Subject: Re: Making LUA safe to execute untrusted scripts [replay]
- From: David Jeske <jeske@...>
- Date: 2000年4月19日 10:23:50 -0700
On Wed, Apr 19, 2000 at 10:26:43AM -0300, Roberto Ierusalimschy wrote:
> > eg. "for" keyword instead of a function in Lua.
>
> We forgot to tell: Lua will have a "for"! (next week)
What will the style of the for be?
One of things which I like most about Python is the simple list based
"for". It's responsible for preventing lots of bugs IMO. However, I
noticed a snafu with doing this kind of thing in Lua, namely that
there dosn't seem to be a "next" tag method.
-- For example, given a Python-esq looping structure like:
a = { 5, 6, 2 };
for num in a do
print num;
end
-- you could have python style number loops based on a table/list,
-- if you had a "next" tag.
function range_next(table,curindex)
if curindex == nil then
return table['start'];
end
if curindex >= table['max'] then
return nil;
end
return (curindex + 1);
end
range_tag = newtag()
settagmethod(range_tag, "next", range_next)
function range(max)
loop_parms = { start = 0, max = max};
settag(loop_parms, range_tag);
return loop_parms;
end
for num in range(4) do
print num
end
---------------------------------------
-- I'm not as fond of the C style number loops
-- because they are so prone to errors:
a = { 1, 2, 3 }
len_a = length(a)
for (x=0; x=x+1; x< len_a) do
print num
end
-- although at least you can do this:
a = {1, 2, 3}
for (num=next(a);num=next(a,x); num!=nil) do
print num
end
-- With only basic number style loops, iteration will
-- be somewhat strange IMO. Witness the example below:
a = { 5, 6, 2 ; val = "this will cause weird behavior" }
len_a = length(a) -- 4
for num = 1 to length(a) do
print a[num]
end
-- outputs: 5, 6, 2, nil
--
David Jeske (N9LCA) + http://www.chat.net/~jeske/ + jeske@chat.net