lua的split函数

function split(s, delim)
    if type(delim) ~= "string" or string.len(delim) <=  then
        return
    end

    local start =
    local t = {}
    while true do
    local pos = string.find (s, delim, start, true) -- plain find
        if not pos then
          break
        end

        table.insert (t, string.sub (s, start, pos - ))
        start = pos + string.len (delim)
    end
    table.insert (t, string.sub (s, start))

    return t
end