Bridge

--Builds a platform or fills a non flat surface.
--place turtle on last block before the span
--this is my first lua app ;)
--this may be upgraded to predetermine length needed for unknown span or wider path etc.

local function block()
    if not turtle.detectDown() then
        turtle.placeDown()
    end
end

local function move()
    if turtle.detect() then
        turtle.dig()
    end
    turtle.forward()
end

local tArgs = { ... }
if #tArgs < 1 then
    print( "Usage: bridge <length> <width>" )
    return
end

local length = tonumber( tArgs[1] )
if length < 1 then
    print( "Bridge length must be positive." )
    return
end

local width = 1
if #tArgs == 2 then
    width = tonumber( tArgs[2] )
    if width < 1 then
        print( "Bridge width must be positive." )
        return
    end
end

local blocks = 0
for n=1,16 do
    blocks = blocks + turtle.getItemCount(n)
end
if blocks < length * width then
    print( "There must be at least "..(length * width).." blocks in the slots." )
    return
else
    local slot = 1
    local right = true
    move()
    block()
    for x=1,width do
        for z=1,length - 1 do
            while turtle.getItemCount(slot) < 1 do
                slot = slot + 1
            end
            turtle.select(slot)
            move()
            block()
        end
        if x ~= width then
            if right then
                turtle.turnRight()
                move()
                turtle.turnRight()
            else
                turtle.turnLeft()
                move()
                turtle.turnLeft()
            end
            sleep(0.1)
            block()
            right = not right
        end
    end
end