what is wrong with my code?

--[[
Made by Dcleondc
8x8 farm
--]]
function turnRight()
    turtle.turnRight()
    turtle.moveForward()
    turtle.turnRight()
end
function turnLeft()
    turtle.turnLeft()
    turtle.moveForward()
    turtle.turnLeft()
end

function farm()
    turtle.digDown()
    turtle.select(1)
    turtle.placeDown()
    turtle.moveForward()
end
function done()
    turtle.select(16)
    while turtle.compareDown() do
    if turtle.compareDown() then
		    farm()
    else
		    turtle.moveForward()
    end
    end
end
for i=1,2 do
    for o=1,8 do
	    done()
    end
    turnRight()
    for p=1,8 do
	    done()
    end
    turnLeft()
end

test:9: attempt to call nil