wall programm for mining turtle

wall.lua

local width = 0
local height = 0

local locX = 1;
local locZ = 1;
local locY = 0;

local removedTop = false;

if #arg == 2 then
    width = tonumber(arg[1]) - 1
    height = tonumber(arg[2])
else
    print('usage: wall <width> <height>')
    return
end

function SelectSlot()
    for slot = 2, 14 do
        if turtle.getItemCount(slot) > 0 then
            turtle.select(slot);
            return true
        end
    end
    removedTop = false
    print('waiting for blocks...');
    if turtle.getItemCount(16) > 0 then
        if turtle.detectUp() then
            turtle.select(15)
            turtle.digUp()
            removedTop = true
        end
        turtle.select(16)
        turtle.placeUp()
        for slot = 2, 14 do
            if turtle.getItemCount(slot) == 0 then
                turtle.select(slot);
                turtle.suckUp()
            end
        end
        turtle.select(16)
        turtle.digUp()
        if removedTop then
            turtle.select(15)
            turtle.placeUp()
        end
    end
    return false;
end

function VerifyFuel()
    if turtle.getFuelLevel() > 10 then return true end
    if turtle.getItemCount(1) > 1 then
        turtle.refuel(1)
        return true
    else
        print('waiting for fuel...')
        return false;
    end
end

function Clear()
    term.clear()
    term.setCursorPos(1,1)
end

function ChangeDirection()
    turtle.turnRight()
    turtle.forward();
    locZ = locZ + 1
end

while not VerifyFuel() do sleep(1) Clear() end
turtle.forward()

if turtle.getItemCount(15) > 0 then
    turtle.select(15)
    turtle.drop()
    turtle.select(1)
end

while locX <= width do
    locY = 0;
    while locY < height do
        if turtle.detectDown then
            turtle.select(15)
            turtle.digDown()
            turtle.drop()
            turtle.down()
        else
            turtle.down()
        end
        locY = locY + 1
    end

    -- fill empty blocks found
    while locY > 0 do
        while not SelectSlot() do sleep(1) Clear() end
        turtle.up()
        if not turtle.placeDown() then 
            turtle.drop()
        end
        locY = locY - 1
    end

    while not VerifyFuel() do sleep(1) Clear() end
    if locX == width then
        if locZ == 4 then Clear() print('Successfully complettet wall') return end
        ChangeDirection()
        locX = 1
    else
        if turtle.detect() then 
            turtle.select(15)
            turtle.dig() 
            turtle.drop()
        end
        turtle.forward()
        locX = locX + 1
    end
end