while

You can make code loop by using while condition do ... end - the test is done at the start of the loop, so if the test fails the loop may not be executed at all.

while danger_threatens () do
  flash_lights ()
end  -- while

If you want to leave the loop from inside you can use a break statement:

while danger_threatens () do
  flash_lights ()
  if enough_flashing () then
    break
  end -- if
end  -- while

The only conditions that are false are the values false and nil - every other value is considered true.

If you want to test at the end of the loop use repeat instead.