gistfile1.lua

local grass_gen = function( minp, maxp )
        if maxp.y < 40 then
                for lx = minp.x, maxp.x do
                        for ly = minp.y, maxp.y do
                                for lz = minp.z, maxp.z do
                                        local p = { x = lx, y = ly, z = lz }
                                        local n = minetest.env:get_node( p )
					minetest.env:add_node( p, { name = "default:dirt_with_grass" } )
                                        end
                                end
                        end
                end
        end
end

minetest.register_on_generated( grass_gen )