Single attempt tunneller v3

local slots=16
local allFullUp=false

-- MoveUp, digging if necessary, but not removing the item in slot 2 (torches)
function MoveUp()
  if turtle.detectUp() then
    turtle.select(2)
    if not turtle.compareUp() then
      turtle.digUp()
    end
  end
  turtle.up()
end

-- MoveForward, digging if necessary, but not removing the item in slot 2 (torches)
function MoveForward()
  while turtle.detect() do
    turtle.select(2)
    if not turtle.compare() then
      turtle.dig()
    else
      break
    end
  end
  return turtle.forward()
end

function DetectAllFull()
  allFullUp=true
  for n=1, slots, 1 do
    if turtle.getItemCount(n) == 0 then
      allFullUp=false
    end
  end
  return allFullUp
end

function GoneFarEnough()
  local Result=true
  if turtle.detectDown() then
    Result = DetectAllFull()
  end
  if Result then
    print("Return to base")
  end
  return Result
end

function OnStopBlock()
  turtle.select(1)
  return turtle.compareDown()
end

-- We should stop if we've moved out into the air or we're on top of the stop block (in slot 1)
function ShouldStop()
  return not turtle.detectDown() or OnStopBlock()
end

function ReturnBecauseAllFullUp()
  print("So much stuff!")
  while not turtle.detectDown() and turtle.forward() do
  end
  turtle.down()
  print("Nearly home")
  while not OnStopBlock() and turtle.forward() do
  end
end

function ReturnBecauseEndOfRun()
  print("My work here is done")
  while not DetectAllFull() and not OnStopBlock() do
    MoveForward()
  end
  if allFullUp then
    turtle.up()
    ReturnBecauseAllFullUp()
  end
end

while not ShouldStop() and turtle.forward() do
  print("Hi Ho, hi ho...")
end
if turtle.detectDown() then
  print("It's up to work I go")
  MoveUp()
  while not turtle.detect() do
    turtle.forward()
  end
  while not GoneFarEnough() do
    MoveForward()
  end
  turtle.turnRight()
  turtle.turnRight()
  if allFullUp then
    ReturnBecauseAllFullUp()
  else
    turtle.digDown() -- Just to be sure
    turtle.down()
    ReturnBecauseEndOfRun()
  end
else
  print("Weird, this one's already done!")
  turtle.turnRight()
  turtle.turnRight()
  ReturnBecauseEndOfRun()
end
-- reset to normal starting position
turtle.turnRight()
turtle.turnRight()
turtle.forward()