Turtlebot Stairway 0.3

test = true
orientation = 0
depth = 0

turtle.refuel()

function isInteresting()
    interesting = false
    if turtle.detect() then
        common = false
        for i=1,6 do -- cobble,stone,dirt,sandstone,sand,gravel
            turtle.select(i)
            common = common or turtle.compare()
        end
        interesting = not common
    end

    if interesting then print("There is something interesting.") end
    return interesting
end

function isInterestingDown()
    interesting = false
    if turtle.detectDown() then
        common = false
        for i=1,6 do -- cobble,stone,dirt,sandstone,sand,gravel
            turtle.select(i)
            common = common or turtle.compareDown()
        end
        interesting = not common
    end

    if interesting then print("There is something interesting below.") end
    return interesting
end

function isInterestingUp()
    interesting = false
    if turtle.detectUp() then
        common = false
        for i=1,6 do -- cobble,stone,dirt,sandstone,sand,gravel
            turtle.select(i)
            common = common or turtle.compareUp()
        end
        interesting = not common
    end

    if interesting then print("There is something interesting above.") end
    return interesting
end

function carefulDescent()
    fall = false
    blocked = turtle.detectDown()
    if blocked then turtle.digDown() end
    descent = turtle.down()
    if descent then depth = depth + 1 end
    if not turtle.detectDown() then fall = true end
    if fall then print("Fall below.") end
    return not fall and descent
end

function carefulAdvance()
    fall = false
    while turtle.detect() do turtle.dig() end
    advance = turtle.forward()
    if not turtle.detectDown() then fall = true end
    if fall then print("Fall ahead.") end
    return not fall and advance
end

function goBack()
    success = false
    while orientation > 0 do
        turtle.turnLeft()
        orientation = orientation - 1
    end

    while depth > 0 do
        repeat
            retreat = turtle.back()
        until not retreat
        success = turtle.up()
        depth = depth - 1
    end
    repeat
        retreat = turtle.back()
    until not retreat
    return success
end

while turtle.getFuelLevel() > (depth * 4) do
    warning = false
    c=1
    while c<4 do
        warning = isInterestingUp()
        warning = isInterestingDown()
        while turtle.detectUp() do turtle.digUp() end
        if not warning then carefulAdvance() else break end
        for d=1,4 do
            if not warning then
                turtle.turnRight()
                orientation = (orientation + 1) % 4
                warning = isInteresting()
            else
                break
            end
        end
        c = c+1
    end
    if not warning then turtle.back() end
    if not warning then warning = not carefulDescent() end
    if warning then break end
end

goBack()