Re: Is Lua used as a data representation language?

[Daurnimator <quae@...>]

On 9 January 2013 04:10, Roberto Ierusalimschy <roberto@inf.puc-rio.br> wrote:
>> On Tue, Jan 8, 2013 at 5:31 PM, Ashwin Hirschi <lua-l@reflexis.com> wrote:
>> > It doesn't seem to handle a simple case like:>
>> >         while 1 do end
>>
>> OK, thanks - I'll try to close some more gaps.  The approach here is
>> static checking, unlike the runtime limits Roberto suggests.
>
> Another runtime aproach is this:
>
> function loaddata (data)
>   local f = assert(loadstring("return (" .. data .. ")"))
>   local count = 0
>   debug.sethook(function ()
>     count = count + 1
>     if count >= 2 then error"cannot call functions" end
>   end, "c")
>   local res = f()
>   count = 0
>   debug.sethook()
>   return res
> end
>
> It only allows expressions (no variables, no assignments) and disallows
> any kind of function calls.
>
> -- Roberto
>

Don't forget to use a pcall (and the pcall counts as a call)!
Even if you wanted to through an error, you'd need to unset the hook.

function loaddata (data)
  local f = assert(loadstring("return (" .. data .. ")"))
  local count = 0
  debug.sethook(function ()
    count = count + 1
    if count >= 3 then
        error"cannot call functions"
    end
  end, "c")
  local ok, res = pcall(f)
  count = 0
  debug.sethook()
  return ok, res
end