tunnel

local x = 1

function df()     -- Dig forward on block
   turtle.dig()
   turtle.forward()
   turtle.digUp()
   turtle.digDown()
end

function line()   -- Dig a line x blocks long
   for i = 1,x do
      df()
   end
end

function leftAround()   --turn around to the left
   turtle.turnLeft()
   df()
   turtle.turnLeft()
end

function rightAround()    --turn around to the right
   turtle.turnRight()
   df()
   turtle.turnRight()
end

function reverse()        --does a full 180 in the same block
   turtle.turnLeft()
   turtle.turnLeft()
end

function layer()      --digs a plane 3 blocks wide
   line()
   leftAround()
   line()
   rightAround()
   line()
end

function round()     --moves one layer down and does a 180
   turtle.down()
   reverse()
end


-- Main Function --

term.write("Depth = ")  --gets x from the user
x = tonumber(read())

layer()                 --hard coded tunnel

round()
for i = 1,x do           --returns to the beginning of the tunnel
   turtle.forward()
end
turtle.turnLeft()
turtle.forward()
turtle.turnRight()