local Scanner = class_createclass()

class_setprotobase(Scanner, {
    -- Obs.: isso não é lexer de verdade a-a
    lex = function(self)
        print('Executando lexer ('..self.valor..')')
    end
})

class_setconstructor(Scanner, function(Scanner, valor)
    local s = class_createinstance(Scanner)
    s.valor = valor
    return s
end)

-- ## Testando

Scanner(40):lex()

local env_getmetatable, env_setmetatable =
          getmetatable,     setmetatable;

-- # Class

-- ## Class functions and helpers

-- Creates an empty class and return itself as a table.

local function class_createclass() return env_setmetatable({ proto = {} }, {}) end

-- Creates an instance of a class.

local function class_createinstance(C) return env_setmetatable({}, C.proto) end

-- Constructs the super class of a class.

local function class_constructsuper(C) return env_setmetatable(env_getmetatable(C).__index(),
  C.proto) end

-- Checks if a value is instance of a class.

local function class_owns(value, C)
  local m = env_getmetatable(value);
  if (not m) then return false end;

  local proto = C.proto;

  while (proto) do
    if (m == proto) then return true end;

    -- Continue checking the prototype of parent classes
    -- until they end.

    proto = env_getmetatable(proto);
    proto = proto and proto.__index;
  end

  return false;
end

-- Sets the constructor of a class.

local function class_setconstructor(C, f) env_getmetatable(C).__call = f end

-- Sets the prototype base of a class.

local function class_setprotobase(C, b)
  C.proto.__index = b;

  -- Merge super prototype base.

  local Super = env_getmetatable(C);
  if (Super) then env_setmetatable(b, Super.proto) end;
end

-- Sets the super (base) class of a class.

local function class_setsuperclass(CA, CB)
  env_setmetatable(CA.proto.__index, CB.proto);
  env_getmetatable(CA).__index = CB;
end