sprinkle

itemSlot = 16

x = 0
y = 0
z = 0

-- The following 'face' directions are relative to the starting position of the turtle in this program

north = 0
west = 1
south = 2
east = 3

face = north

length = 9
width = 9

interval = 4

args = {...}
nArgs = #args

if nArgs == 0 or (nArgs == 1 and args[1]== "help") then
	print("Lays down a pattern of items of length and width.")
	print("Usage: sprinkle <length> <width>")
	return
end

if nArgs ~= 2 then
  print("Usage: sprinkle <distance>")
  return
end

length = tonumber(args[1])
if length == nil then
  print("\"", args[1], "\" is not a valid length")
  return
end
if length < 1 then
  print("length must be a positive number greater than zero")
  return
end

width = tonumber(args[2])
if width == nil then
  print("\"", args[1], "\" is not a valid width")
  return
end
if width < 1 then
  print("width must be a positive number greater than zero")
  return
end

function left()
 if face == 0 then face = 1 turtle.turnLeft() return end
 if face == 1 then face = 2 turtle.turnLeft() return end
 if face == 2 then face = 3 turtle.turnLeft() return end
 if face == 3 then face = 0 turtle.turnLeft() return end
 print("function left\(\): Bad face value: ", face)
end

function right()
 if face == 0 then face = 3 turtle.turnRight() return end
 if face == 1 then face = 0 turtle.turnRight() return end
 if face == 2 then face = 1 turtle.turnRight() return end
 if face == 3 then face = 2 turtle.turnRight() return end
 print("function right\(\): Bad face value: ", face)
end

function setFace(f)
	if f == 0 then
	  if face == 0 then return end
	  if face == 1 then right() return end
	  if face == 2 then right() right() return end
	  if face == 3 then left() return end
	end

	if f == 1 then
	  if face == 0 then left() return end
	  if face == 1 then return end
	  if face == 2 then right() return end
	  if face == 3 then right() right() return end
	end

	if f == 2 then
	  if face == 0 then left() left() return end
	  if face == 1 then left() return end
	  if face == 2 then return end
	  if face == 3 then right() return end
	end

	if f == 3 then
	  if face == 0 then right() return end
	  if face == 1 then left() left() return end
	  if face == 2 then left() return end
	  if face == 3 then return end
	end
end

function forward(nBlocks)
	for i=1,nBlocks do
		turtle.forward()
	end

  	if face == north then z = z+nBlocks return end
  	if face == west then x = x-nBlocks return end
  	if face == south then z = z-nBlocks return end
  	if face == east then x = x+nBlocks return end

end

function layRow(nBlocks)
	turtle.select(itemSlot)

	for i=0,nBlocks do
		if (i % interval) == 0 then
			turtle.placeDown()
		end
		if i < nBlocks then
			forward(1)
		end
	end
end

function layPattern(l, w)

--	setFace(north)
	layRow(w - 1)

	setFace(west)
	layRow(l - 1)

	setFace(south)
	layRow(w - 1)

	setFace(east)
	layRow(l - 1)

	setFace(north)
end

radius = interval

--	Let's let the parent program get to start position

--[[
turtle.up()

turtle.select(itemSlot)
turtle.placeDown()

-- Move to starting position

setFace(north)
forward(radius)
setFace(west)
forward(radius)
--]]

layPattern(length, width)

setFace(north)