ComputerCraft Simple Tree Farm Script

a = ...
local size = a or 10
local timer = 0
local blocks = {
    'log',
    'blockRubWood'
}
local saplings = {
    'sapling',
    'chest',
    'torch'
}

function checkSapling(s)
    s = s:lower()
    local a = false
    for i, p in ipairs(saplings) do
        a = a or string.find(s, p:lower())
    end
    return a
end

function digForward()
    while not turtle.forward() do
        turtle.dig()
    end
end

function match(s)
    s = s:lower()
    local a = false
    for i, p in ipairs(blocks) do
        a = a or string.find(s, p:lower())
    end
    return a
end

function harvestTree()
    local height = 0
    turtle.digDown()
    while turtle.detectUp() do
        turtle.digUp()
        if turtle.up() then
            height = height + 1
        end
    end
    for i = 1, height do
        while not turtle.down() do turtle.digDown() end
    end
end

turtle.select(1)
while true do
    local right = true
    for x = 1, size do
        for y = 1, size do
            turtle.suckDown()
            if ((not turtle.detectDown()) and (turtle.getItemCount(1) > 1)) then
                turtle.placeDown()
            end
            local a, data = turtle.inspectUp()
            if a and match(data.name) then
                harvestTree()
            else
                local b, data2 = turtle.inspectDown()
                if b and not checkSapling(data2.name) then
                    turtle.digDown()
                end
                if a then turtle.digUp() end
            end

            digForward()
        end
        if right then
            turtle.turnRight()
            digForward()
            turtle.turnRight()
        else
            turtle.turnLeft()
            digForward()
            turtle.turnLeft()
        end
        right = not right
        digForward()
    end
    if right then
        turtle.turnLeft()
    else
        turtle.turnRight()
    end
    for i = 1, size do
      digForward()
    end
    if right then
        turtle.turnRight()
    else
        turtle.turnLeft()
    end
    local a, data = turtle.inspectDown()
    if a and string.find(data.name:lower(), 'chest') then
        for i = 2, 16 do
            turtle.select(i)
            turtle.dropDown(64)
        end
    end
    sleep(timer)
end