The problem with stack-based environments...

[Mark Hamburg <mark@...>]

As the primary proponent of stack-based-environments -- though I will identify myself less as a proponent and more as someone who has tried get clarity around what in-do-end seems to be implying (as opposed to what it actually does) -- I need to call out the biggest problem that's occurred to me with them:

While sandboxing itself is easy:

	in sandbox do
		sandboxed_function()
	end

If the sandbox generates an object or a callback for later use:

	local plugin
	in sandbox do
		plugin = plugin_loader()
	end

We need to decide what to do when we later invoke a method on the object or invoke the callback. A straight call as in:

	plugin:method()

will not get sandboxed. We can certainly wrap it up in an appropriate sandboxing construct, but that's going to be a pain to remember to do and its going to be awkward in places where we want to work with the results of the method call since in-do-end is not an expression.

Furthermore, we may not want it always wrapped. If we are exploiting the stack-based environments for i/o redirection, for example -- a standard use case -- then we probably want that redirection preserved into the method call.

I don't have a proposed resolution at this time that would resolve this tension.

Mark