AVeryGoodCounter.lua

local Counter = setmetatable({}, {
  __call = function(self, args)
    return setmetatable({n = type(args) == "table" and -1 or 1}, {
      __call = function(self, args, ...)
        if type(args) == "table" then
          self.n = self.n - 1
        elseif type(args) == "string" then
          self.n = self.n * 2
        else
          self.n = self.n + 1
        end
        return self
      end,
      __tostring = function(self)
        return tostring(self.n)
      end
    })
  end
})

print(Counter()) -- 1
print(Counter()()) -- 2
print(Counter()()()()()()()()()()()()()()()()()()) --18
print(Counter{}{}{}{}) -- -4
print(Counter{}(){}()) -- 0
print(Counter()()"""""""") -- 32
print(Counter()(){}""""{}()) -- 5