Frame Filler (for a flooring work)

-- #########################
-- Frame Filler (for a flooring work)
-- version0.1
-- http://hevohevo.hatenablog.com/

-- 1. Build a frame for a flooring work
--    The frame must be a rectangle
-- 2. Set the turtle on the frame-block as follows;

-- Top view
-- T: turtle, f: frame-blocks (e.g., stone-brick)
-- fffffffffffffffffffff
-- f                   f
-- f                   f
-- fTfffffffffffffffffff

-- 3. Insert Frame-blocks (stone-brick) into turtle's slot 15
--    for detecting a boundary line
-- 4. Slot 1-14 are used for filling blocks
-- 5. Run this program

FRAME = 15
FUEL = 16

function select_block(slot)
  slot = slot or turtle.getSelectedSlot()
  if turtle.getItemCount(slot) == 0 then
    if slot < 14 then
      select_block(slot+1)
    else
      error("Item empty: insert slots 1-14.")
    end
  else
    turtle.select(slot)
  end
end

function detect_frame()
  local tmp_slot = turtle.getSelectedSlot()
  turtle.select(FRAME)
  local status, err = turtle.compareDown()
  turtle.select(tmp_slot)
  return status, err
end

-- main
turtle.select(1)
local count = 0
while true do
  turtle.forward()
  if detect_frame() then
    count = count +1
    turtle.back()
    turtle.turnRight()
    if count > 2 then break end
  else
    count = 0
    select_block()
    turtle.placeDown()
  end
end