ComputerCraft TreeFarm

-- tree farmer
-- requires a very specific tree farm setup
--   which I will document somewhere and
--   put a link to when that's done
-- put fuel in first slot
-- put 1 block of wood type in second slot
-- put saplings of wood type in third slot

function fuel()
  if turtle.getFuelLevel() < 30 then
    turtle.select(1)
    if turtle.refuel(1) then
      return true
    end
    print("Refuelling failed.")
    return false
  end
end

function chop ()
  local blocksMovedUp = 0
  while turtle.detect() do
    turtle.dig()
    if turtle.detectUp() then
      turtle.digUp()
    end
    turtle.up()
    blocksMovedUp = blocksMovedUp + 1
  end
  while blocksMovedUp > 0 do
    turtle.down()
    blocksMovedUp = blocksMovedUp - 1
  end
  -- plant new tree
  turtle.select(3)
  turtle.place()
  return true
end

function goNext()
  i = 1
  for i=1,4,1 do
    turtle.forward()
  end
  turtle.turnLeft()
  -- has the tree grown?
  ret = false
  while ret == false do
    ret = detectTree()
  end
end

function detectTree()
  turtle.select(2)
  if turtle.compare() then
    return true
  else
    return false
  end
end

function farmTree()
  goNext()
  chop()
end

-- farms the entire treefarm
function treeFarm()
  side = 0
  for side=1,4,1 do
    for tree=1,2,1 do
      farmTree()
      turtle.turnRight()
    end
    turtle.turnRight()
  end
end

function dump()
  for i=4,16,1 do
    turtle.select(i)
    turtle.drop()
  end
end

-- keep farming trees until...
while true do
  if fuel() == false then
    print('Ran out of fuel')
    break
  end
  treeFarm()
  dump()
  -- if there are no more saplings
  if turtle.getItemCount(3) < 8 then
    print('Ran out of saplings')
    break
  end
end