badfile.lua

while 1 do
    print("", "badfile")
end

preempt.lua

function sandbox(fn)
    -- read script and set the environment
    f = loadfile(fn, "t")
    debug.setupvalue(f, 1, {print = print})

    -- create a coroutine and have it yield every 50 instructions
    local co = coroutine.create(f)

    function mhook()
      print("hooked")
      print(debug.getinfo(co, 0))
      co.yield()
    end

    debug.sethook(co, mhook, "", 1)

    -- demonstrate stepped execution, 5 'ticks'
    for i = 1, 50 do
        print("tick")
        print(coroutine.status(co))
        coroutine.resume(co)
    end
end

sandbox("badfile.lua")