Vector

function vector(x, y, z)
    local v = {
        x = x or 0,
        y = y or 0,
        z = z or 0,
        __add = function (o)
            return vector(
                x + o.x,
                y + o.y,
                z + o.z
            )
        end,
        __sub = function (o)
            return vector(
                x - o.x,
                y - o.y,
                z - o.z
            )
        end,
        __mul = function (o)
            return vector(
                x * o.x,
                y * o.y,
                z * o.z
            )
        end,
        dot = function(o)
            return x*o.x + y*o.y + z*o.z
        end,
        cross = function(o)
            return vector(
                y*o.z - z*o.y,
                z*o.x - x*o.z,
                x*o.y - y*o.x
            )
        end,
        __len = function()
            return math.sqrt( x*x + y*y + z*z )
        end,
        round = function()
            return vector(
                math.floor( x + 0.5 ),
                math.floor( y + 0.5 ),
                math.floor( z + 0.5 )
            )
        end,
        __tostring = function()
            return x..","..y..","..z
        end,
        __eq = function (o)
            return x == o.x and y == o.y and z == o.z
        end
    }

    function v.__unm()
        return v.mul(-1)
    end

    function v.normalize()
        return v.mul( 1 / v.length() )
    end

    v.add = v.__add
    v.subtract = v.__sub
    v.sub = v.__sub
    v.multiply = v.__mul
    v.mul = v.__mul
    v.length = v.__len
    v.len = v.__len
    v.tostring = v.__tostring
    v.equals = v.__eq
    v.eq = v.__eq

    v.__metatable = v

    function v.__newindex()

    end

    return setmetatable(v, v)
end