gistfile1.txt

local handlers = setmetatable({}, { __index = function(self, k) self[k] = {}; return self[k]; end; })

event = {}

function event.add(name, fn)
  assert(handlers[name][fn] == nil, "attempt to register the same callback multiple times for event " .. name)
  handlers[name][fn] = true
  return fn
end

function event.remove(name, fn)
  assert(handlers[name][fn], "attempt to unregister a non-registered callback for event " .. name)
  handlers[name][fn] = nil
end

function event.call(name, ...)
  for handler in pairs(events[name]) do
    handler(...)
  end
end