Make sure that callbacks aren't invoked more than once

monarch/utils/async.lua

@@ -0,0 +1,47 @@
+local M = {}
+
+local NOT_STARTED = "not_started"
+local YIELDED = "yielded"
+local RESUMED = "resumed"
+local RUNNING = "running"
+
+function M.async(fn)
+	local co = coroutine.running()
+	
+	local state = NOT_STARTED
+
+	local function await(fn, ...)
+		state = RUNNING
+		fn(...)
+		if state ~= RUNNING then
+			return
+		end
+		state = YIELDED
+		local r = { coroutine.yield() }
+		return unpack(r)
+	end
+
+	local function resume(...)
+		if state ~= RUNNING then
+			state = RUNNING
+			local ok, err = coroutine.resume(co, ...)
+			if not ok then
+				print(err)
+				print(debug.traceback())
+			end
+		end
+	end
+
+	if co then
+		return fn(await, resume)
+	else
+		co = coroutine.create(fn)
+		return resume(await, resume)
+	end
+end
+
+return setmetatable(M, {
+	__call = function(t, ...)
+		return M.async(...)
+	end
+})