Bank

-- Bank class
-- notice NO module(package.seecrap)

local _M = {}  -- class table, which is returned at the end


-- properties
_M.gold = 100    -- initial capital
_M.silver = 50


-- methods
-- notice NO "local" and colons (:)
-- those functions are methods of table _M and they use "self"

function _M:withdraw(account, amount)
    self[account] = self[account] - amount
    return amount
    -- this is a faulty bank code, don't use it in real life
end

function _M:deposit(account, amount)
    self[account] = self[account] + amount
end



-- you can also use this as an exchange library
-- notice NO "local" and a DOT (.) and no use of "self"

function _M.gold2silver (amount)
    return amount * 2
end


-- when you require this thing you do    bank = require("bank") and _M comes into "bank" variable
return _M


-- After you require you can use  bank:deposite('silver', bank.gold2silver(bank.gold))  - which will convert all gold into silver inside the bank. Deposite is a method and gold2silver is a simple conversion function (supplimentary).