Turtle Automatic Tree Farm - Computercraft Lua

--[[ Running this script on a turtle with saplings in slot 1, bone-meal in slot 2 and coal in slot 16 and a chest behind the turtle for the wood drop off point will create an automatic tree farm. combining this with a chest to the left of the turtle for sapling replenishment and chest to the right for coal replenishment will ensure a long running automated process.]]

-- This function lays saplings and applies bone-meal
function plant()
    turtle.select(1)                --selects sapling
    turtle.place()                  --places sapling
    turtle.select(2)                --selects bone-meal
    turtle.place()                  --fertilizes sapling
    turtle.suck()                   --picks up any saplings that have fallen
end

-- This function checks fuel level and refuels
function fuel()
    if turtle.getFuelLevel() < 50 then      --checks fuel level and refuels
        turtle.select(16)
        turtle.refuel(5)            --picks up any saplings that have fallen
    end
    print( turtle.getFuelLevel() .. " fuel left.")  --displays fuel level to user
end

-- This function cuts a column directly above the turtle and then returns to ground level
function column()
    while turtle.detectUp() == true do      --cut tree down
        turtle.digUp()
        turtle.up()
        turtle.suck()               --picks up any saplings that have fallen
    end
    while turtle.detectDown() == false do       -- return to ground level
        turtle.down()
        turtle.suck()               --picks up any saplings that have fallen
    end
end

-- This function moves from start position, runs column and returns to start position
function fell()
    turtle.dig()                    --breaks bottom block of tree
    turtle.forward()                --move into gap
    column()                    --run column function
    turtle.turnRight()              --return to start
    turtle.turnRight()
    turtle.forward()
end

-- This function empties all collected wood into chest, checks sapling and fuel supplies and restocks
function empty()
    for j = 3, 15 do                -- empty slots 3 to 15 into chest
        turtle.select(j)
        turtle.drop()
    end
    turtle.turnLeft()
    if turtle.getItemCount(16) < 5 then     -- replenish fuel stocks
        turtle.select(16)
        turtle.suck(10)
    end
    turtle.turnLeft()
    if turtle.getItemCount(1) < 5 then      --replenish sapling stocks
        turtle.turnLeft()
        turtle.select(1)
        turtle.suck()
        turtle.turnRight()
    end
end

-- This function checks to see if the sapling has been fertilized into a full tree
function compare()
    turtle.select(1)
    if turtle.compare() == true then
        return true -- false could indicate that there is no bonemeal or saplings
    else
        return false
    end
end

-- This block triggers the appropriate functions in the correct order.
repeat                          --start loop
    fuel()                      --check fuel
    plant()                     --plant and fertilize tree
    fuel()                      --check fuel again
    if compare() == false then          --if tree has grown cut down tree
        fell()
    else                        --if tree hasn't grown display error
        print("error")
        repeat
            sleep(1)
            turtle.select(2)
        until turtle.getItemCount() > 20    --this will terminate script
    end
    empty()                     --empty harvest and restock fuel and materials
until 1 > 2                     -- always false creating infinite loop