The coroutine stack

A coroutine + callstack-based stack of varargs in pure Lua. Inspired by this tweet.

Note: Currently, for the sake of simplicity, only a single stack is implemented. By parameterizing each function in terms of the stack, multiple stacks could be implemented, but this is not for practical purposes (in practice, you should usually use tables paired with table.insert and table.remove instead, unless your problem lends itself well to a recursive solution; keep stack overflows in mind though).

local function new_entry(...)
	local cmd_
	local function process_cmd(cmd, ...)
		cmd_ = cmd
		if cmd == "push" then
			return process_cmd(new_entry(...))
		end
	end
	repeat
		process_cmd(coroutine.yield())
	until cmd_ == "pop"
	return coroutine.yield(...)
end

local stack = coroutine.create(function(cmd, ...)
	while true do
		assert(cmd == "push", "empty stack")
		new_entry(...)
	end
end)

local function push(...)
	assert(coroutine.resume(stack, "push", ...))
end

local function retvals(status, ...)
	local potential_error = ...
	assert(status, potential_error)
	return ...
end

local function pop()
	return retvals(coroutine.resume(stack, "pop"))
end

-- Tests

do
	push(1, 2, 3)
	push(4, 5, 6)
	local a, b, c = pop()
	assert(a == 4 and b == 5 and c == 6)
	a, b, c = pop()
	assert(a == 1 and b == 2 and c == 3)
	for i = 1, 1000 do
		push(i)
	end
	for i = 1000, 1, -1 do
		assert(pop() == i)
	end
end