lua实现string的split功能

function split(str,sp)
    local result = {}
    local i = 0
    local j = 0
    local num = 1
    local pos = 0
    while true do
        i , j = string.find(str,sp,i+1)
        if i == nil then 
            if num ~=1 then
                result[num] = string.sub(str,pos,string.len(str))
            end
            break 
        end
        result[num] = string.sub(str,pos,i-1)
        pos = i+string.len(sp)
        num = num +1
    end
    return result
end