CC Turtle Fence Builder

local version = 1.1
--  +------------------------+  --
--  |-->  INITIALIZATION  <--|  --
--  +------------------------+  --
if not turtle or not turtle.forceForward then
  print("This program can only be")
  print("executed by a turtle")
  print("with BetterTurtle API.")
  return
end

-- UPDATE HANDLING --
if _UD and _UD.su(version, "5V85iVAM", {...}) then return end

local ARGS = {...}

turtle.select(1)

-- convenience functions
local function nextSlot()
  turtle.select(turtle.getSelectedSlot()+1)
end

local function empty()
   return turtle.getItemCount() == 0
end

local function build()
  turtle.placeDown()
  if empty() then nextSlot() end
  turtle.forceForward()
end


-- MAIN

if not empty() then
  -- build fence
  local w = tonumber(ARGS[1])
  local l = tonumber(ARGS[2])

  turtle.forceUp()
  for i=2,l do build() end
  turtle.turnRight()
  for i=2,w do build() end
  turtle.turnRight()
  for i=2,l do build() end
  turtle.turnRight()
  for i=2,w do build() end

else
  -- take down fence
  while turtle.detect() do
    while turtle.detect() do
      turtle.forceForward()
    end
    turtle.turnRight()
  end
end