lua turtle M2NPV

stop=false
if(turtle.detect()==true)then
    flag = true
else
    flag = false
end
while(stop==false)do
    if(redstone.getInput("back")==true)then
        if(flag==false)then
            turtle.place()
            flag=true
        else
            turtle.dig()
            flag=false
        end
        while(redstone.getInput("back")==true)do
            sleep(0.2)
        end
    end
end