Re: How to avoid "infinite loop"

[Sean Conner <sean@...>]

It was thus said that the Great Elias Barrionovo once stated:
> On Wed, Sep 2, 2015 at 5:36 PM, Rodrigo Azevedo <rodrigoams@gmail.com> wrote:
> > Is Lua a "infinite loop" safe language in any conception? (I really don't
> > know the strategies involved to check/avoid these cases at implementation
> > level)
> 
> 
> Alan Turing famously proved that there is no general way [1] of
> finding out whether a piece of program terminates for an arbitrary
> input without actually running it and hoping for the best. It's known
> as the Halting Problem: https://en.wikipedia.org/wiki/Halting_problem
> 
> However, there are certain heuristics. For instance, you could create
> a graph of branches and function calls and see if there are any
> cycles, but it is very error prone (add some basic metatable or ENV
> trickery and the checker won't work).
> 
> Usually, what is done is to limit the total runtime of a piece of
> code, which in Lua can be done using hooks and the debug library.
> Others in this list may enlight you in this matter.

  This is probably the best way, as there are other ways to fall into an
infinite loop:

	for i = 1 , 1 , 0 do end
	while true do end
	repeat until false
	function a() return a() end a()

  -spc (Recursion:  see recursion)