hare (twitch tv)

function sweep(rows, columns, sweepFunc)
	assert(type(rows) == 'number' and rows >= 1)
	assert(type(columns) == 'number' and columns >= 1)

	-- "forward" is "north" and decreases z
	-- "back" is "south" and increases z
	-- "right" is "east" and increases x
	local x = 0
	local z = 0

	local turnRightNext = true

	-- call the sweep function at the starting point:
	if sweepFunc ~= nil then
		sweepFunc(x, z)
	end

	for curColumn = 1, columns do
		-- move up/down the row:
		for curRow = 2, rows do
			turtle.forward() -- TODO: handle if turtle can't move forward

			-- update the relative z coordinate:
			if turnRightNext then
				z = z - 1
			else
				z = z + 1
			end

			if sweepFunc ~= nil then
				sweepFunc(x, z) -- call the sweep function once per point in the rectangular area
			end
		end

		-- turn and move to the next column
		if curColumn ~= columns then
			if turnRightNext then
				turtle.turnRight()
				turtle.forward() -- TODO: handle if turtle can't move forward
				turtle.turnRight()
			else
				turtle.turnLeft()
				turtle.forward()  -- TODO: handle if turtle can't move forward
				turtle.turnLeft()
			end
			x = x + 1
			if sweepFunc ~= nil then
				sweepFunc(x, z)
			end
			turnRightNext = not turnRightNext -- toggles turning direction
		end
	end

	-- move back to starting point
	local i
	if columns % 2 == 1 then -- when columns is odd, we end at the far end of the rows
		for i = 1, rows-1 do
			turtle.back() -- TODO: handle if turtle can't move back
		end
		turtle.turnLeft()
	else
		turtle.turnRight()
	end

	for i = 1, columns-1 do
		turtle.forward()  -- TODO: handle if turtle can't move forward
	end

	turtle.turnRight() -- face the original direction
end