Computercraft: wall 16x16x4

function findeSlot()
 local i
 for i=1,16 do
  if turtle.getItemCount(i)>0 then
   return i
  end
 end
 return 0
end

function moveN(n)
 local i
 for i=1,n do
  turtle.dig()
  turtle.forward()
 end
end

function moveNplace(n)
 local i
 for i=1,n do
  if turtle.getItemCount(slot)==0 then
   slot=findeSlot()
   if slot==0 then slot=1 end
   turtle.select(slot)
  end
  turtle.placeDown()
  turtle.dig()
  turtle.forward()
 end
end
-------------------
--global variables:
slot=1
turtle.select(slot)
local i
turtle.up()
moveN(1)
turtle.turnRight()
for i=1,16 do
 moveNplace(15)
 turtle.turnLeft()
 moveNplace(1)
 turtle.turnLeft()
 moveNplace(15)
 turtle.turnRight()
 moveNplace(1)
 turtle.turnRight()
 moveNplace(15)
 turtle.turnLeft()
 moveNplace(1)
 turtle.turnLeft()
 moveNplace(15)
 turtle.turnLeft()
 moveNplace(1)
 turtle.up()
 moveN(2)
 turtle.turnLeft()
end
turtle.turnRight()
moveN(1)
for i=1,17 do
 turtle.down()
end
turtle.turnRight()
turtle.turnRight()