markers

function forward(n)
    for i=1,n do
        if turtle.detect() then
            repeat
                turtle.dig()
            until not turtle.detect()
        end
        turtle.forward()
    end
end

function place()
    if turtle.detect() then
        turtle.digDown()
    end
    turtle.placeDown()
end

function markers(w,h)
    turtle.turnLeft()
    forward(w/2)
    place()
    turtle.turnRight()
    forward(h)
    place()
    turtle.turnRight()
    forward(w)
    place()
    turtle.turnRight()
    forward(h)
    place()
    turtle.turnRight()
    forward(w/2)
end

local args = {...}
if #args==0 then
    print("Usage: markers w [h]")
    return
end
local w,h
if #args==1 then
    w = tonumber(args[1])
    h = w
else
    w = tonumber(args[1])
    h = tonumber(args[2])
end
markers(w,h)