de Casteljau's algorithm in lua metatables

bezier.lua

--[[a parametric function describing the Bezier curve determined by given control points,
    which takes t from 0 to 1 and returns the x, y of the corresponding point on the Bezier curve]]
function bezier(xv, yv)
        local reductor = {__index = function(self, ind)
                return setmetatable({tree = self, level = ind}, {__index = function(curves, ind)
                        return function(t)
                                        local x1, y1 = curves.tree[curves.level-1][ind](t)
                                        local x2, y2 = curves.tree[curves.level-1][ind+1](t)
                                        return x1 + (x2 - x1) * t, y1 + (y2 - y1) * t
                                end
                        end})
                end
        }
        local points = {}
        for i = 1, #xv do
                points[i] = function(t) return xv[i], yv[i] end
        end
        return setmetatable({points}, reductor)[#points][1]
end