A lua script for the ComputerCraft Minecraft mod, that will mine in a spiral pattern, exposing the most blocks, with the least fuel consumed.

spiralMine.lua

-- This work is licensed under a CC BY-NC-SA 3.0 license.
-- http://creativecommons.org/licenses/by-nc-sa/3.0/
-- 
-- by the Forlorn Hedgehog
--
-- Fuel goes in slot 1. Torches go in slot 2. Floor blocks (usually cobblestone) go in slot 3.

-- If fuel level is less than 10, refuel
function fuel()
	if turtle.getFuelLevel() < 10 then
		turtle.select(1)
		if turtle.refuel(1) then
			return true
		end
		print("Refuelling failed.")
		return false
	end
end

-- Place floor block, if there isn't one.
function placeFloorBlock()
	if not turtle.detectDown() then
		turtle.select(3)
		if turtle.placeDown() then
			return true
		end
		print("Placing floor block failed.")
		return false
	end
end

-- Digs and moves into a 1x2x1 (xyz) area.
function basicDigAndMove()
	while not turtle.forward() do
		if not turtle.dig() then
			turtle.attack()
		end
	end
	while turtle.detectUp() do
		turtle.digUp()
		sleep(0.5)
	end
	placeFloorBlock()
end

-- Turn turtle 180 degrees
function turnAround()
	turtle.turnLeft()
	turtle.turnLeft()
end

-- Place torch on floor, in front of the turtle
function placeTorch()
	turtle.select(2)
	if turtle.place() then
		return true
	end
	print("Placing torch failed.")
	return false
end

-- Arguments
local tArgs = {...}
if #tArgs ~= 1 or tonumber(tArgs[1]) == nil or math.floor(tonumber(tArgs[1])) ~= tonumber(tArgs[1]) or tonumber(tArgs[1]) < 1 then
	print("Usage: spiralMine <diameter>")
	return
end

local diameter = tonumber(tArgs[1])

local blocksMoved = 0
function doThings(num_of_things)
	fuel()
	for i=1,num_of_things do
		basicDigAndMove()
		blocksMoved = blocksMoved + 1

		-- Add torch (on floor) every 8 blocks
		if (blocksMoved % 8) == 0 then
			turnAround()
			placeTorch()
			turnAround()
		end
	end
	turtle.turnRight()
	local otherNum = num_of_things - 1
	if otherNum > 0 then
		fuel()
		for i=1,otherNum do
			basicDigAndMove()
			blocksMoved = blocksMoved + 1

			-- Add torch (on floor) every 8 blocks
			if (blocksMoved % 8) == 0 then
				turnAround()
				placeTorch()
				turnAround()
			end
		end
		turtle.turnRight()
		local finalNum = otherNum - 2
		if finalNum > 0 then
			doThings(finalNum)
		end
	end
end

doThings(diameter)