RE: Simple Slideshow - user skip

[RLake@...]

> That’s a very interesting
idea, but I’d really like to run some cleanup code in the same coroutine
when the slideshow is aborted.

Only slightly more difficult. I was
going to suggest this in the first place, but the question at the end seemed
relevant.

coroutine:

  local function cleanup()
    -- do stuff
  end

  register_cleanup(cleanup)

Supporting function (assumes that Wait
is provided):
(This must be a Lua function, otherwise
the yield in Wait won't work)

  function register_cleanup(fn)
    local _wait = Wait
    function Wait(time)
      local thrown =
_wait(time)
      if thrown then
 fn();  error(thrown);  end
    end
  end

Now, if (the original) Wait returns
with a "true" result, the registered cleanup function will be
called, and then the thread will return the result from Wait as an error
result (which you can pick up from lua_resume).

There are many variations on this theme:
one is to provide the thrown object to the cleanup function and let it
return an error object:

  if thrown then error(fn(thrown))
end

Another option would be to allow multiple
cleanup functions, perhaps by keeping a table of them.

However, what might you need to clean
up which could not more reliably be handled by garbage collection?