wall

x = 400

function check()
if d.name ~= "minecraft:dirt" and d.name ~= "miencraft:grass" and d.name ~= "minecraft:stone" and d.name ~= "minecraft:cobblestone" and d.name ~= "minecraft:sand" and d.name ~= "minecraft:gravel" then
return true
else
return false
end
end

function pd()
  s, d = turtle.inspectDown()
  if check() == true then
    turtle.digDown()
    turtle.placeDown()
    s, d = turtle.inspect()
    while check() == false do
    turtle.digUp()
    turtle.up()
    s, d = turtle.inspect()
    end
    while turtle.forward() == false do
    turtle.dig()
    end
    s, d = turtle.inspectDown()
    while check() == true do
      turtle.digDown()
      turtle.down()
      s, d = turtle.inspectDown()
    end
  else
    turtle.digUp()
    turtle.up()
  end
end

while x > 0 do
pd()
end