Convert tabs to spaces while aligning with columns

tabber.lua

local tabsize = 4;
function tabber(s)
        local t = {};
        for part in s:gmatch("[^\t]*") do
                t[#t+1] = part;
                t[#t+1] = "\t";
        end
        t[#t] = nil;
        local n = 0;
        for i=1,#t do
                if i%2 == 0 then -- got a tab
                        t[i] = (" "):rep(tabsize - (n + tabsize) % tabsize + 1);
                end
                n = n + #t[i];
        end
        return table.concat(t);
end