As in, no, it's not a "keep-alive ping" that you need here. More like the opposite.
When you plonk down two computers and open them up, they look and act like two separate computers, each running a Lua interpretor. The truth is that, behind the facade, there's only
one Lua interpretor for your world, no matter how many computers or turtles are in it.
This interpretor treats each system as a separate co-routine. They're boxed off so that they can't interact with each other directly.
Now here's the catch - the interpretor can only run one co-routine at a time. There's no true multitasking going on here - when one of your computers is doing something, the others aren't.
The solution is that every time a co-routine has to pause, the interpretor takes that opertunity to switch to the next one. For example, if a system is waiting for you to type something, or whatever for the next moment on which the cursor blinks, or waiting for a turtle to finish moving… it's
yielding, and this is what allows ComputerCraft to quickly divert processing power to all the systems in your world and maintain the illusion that they're all running at once.
Thing is, it's possible to write code that doesn't pause - for example, you can shove as many "print" statements into your script as you like, Lua will execute all of them and then straight away move on to the next line of the same script. Create an infinite loop that doesn't pause, and ComputerCraft will never see an opportunity to let other systems in the world do anything. This breaks the illusion, as suddenly every system in the world stops working, waiting for that one script to give up control.
For this reason, if a script runs for more then ten seconds without yielding, ComputerCraft will crash that script.
Currently your "testIfDraw()" function, which is called over and over in a loop, reads like this:
function testIfDraw()
if rs.testBundledInput("left", colors.brown) then
drawbridge = not drawbridge
updateDrawbridge()
sleep(1)
end
end
If the colour brown is active to the left, then this will sleep for at least a second every time the loop repeats. If it's not, then the script
never sleeps. There's no pause, and so it'll crash if you don't hit the switch at least once every ten seconds.
You could move/add sleep statements to deal with this, but
os.pullEvent() offers a more elegant solution - you can rig it to specifically pause your script until a redstone input changes.
For example, assuming your drawbridge is being toggled with a button:
function testIfDraw()
-- Sit and wait until the input turns on:
while not rs.testBundledInput("left", colors.brown) do
os.pullEvent("redstone")
if not rs.getInput("top") then error() end -- Quit if the top redstone signal was lost.
end
-- Toggle the bridge:
drawbridge = not drawbridge
updateDrawbridge()
-- Sit and wait until the input turns off, if it hasn't already:
while rs.testBundledInput("left", colors.brown) do os.pullEvent("redstone") end
end
Beats me what the deal with the "out of bounds" error is. Wouldn't be lucky enough to have any more of the error, like an API name or a line number?
