Minecraft ComputerCraft Turtle follow blocks

-- License: Authors Right to Brag
-- You may use this source without restrictions with the exception of boasting.
-- Only Micha may brag about this.

print ("follow v0.1")
print ("Follows a path of whatever the turtle has got in his inventory")
print ("(I recommend using train tracks)")
print ("All Bragging Rights Reserved - Micha 2012")
print ("")

local state = "scan"

function innerscan()
    local somethingDown = false
    local somethingForward = false
    local matchDown = false
    local matchForward = false
    if turtle.detectDown() then
        somethingDown = true
        for i = 1, 9, 1 do
            turtle.select(i)
            if turtle.compareDown() then
                matchDown = true
            end
        end
    end
    if turtle.detect() then
        somethingForward = true
        for i = 1, 9, 1 do
            turtle.select(i)
            if turtle.compare() then
                matchForward = true
            end
        end
    end
    return somethingDown, somethingForward, matchDown, matchForward
end

function upscan()
    local somethingUp = false
    local matchUp = false
    if turtle.detectUp() then
        somethingUp = true
        for i = 1, 9, 1 do
            turtle.select(i)
            if turtle.compareUp() then
                matchUp = true
            end
        end
    end
    return somethingUp, matchUp
end


function scan()
    local somethingDown, somethingForward, matchDown, matchForward = innerscan()
    if not somethingDown then
        state = "toGround"

    else
        if matchDown then
            state = "forwardAndScan"
        else
            if somethingForward then
                if matchForward then
                -- train track up?
                    state = "riseAndScan"
                else
                    turtle.turnLeft()
                end
            else
                turtle.turnLeft()
            end
        end
    end

end

function moveDown()
    local somethingDown, somethingForward, matchDown, matchForward = innerscan()
    if not somethingDown then
        turtle.down()
        return true
    else
        return false
    end
end

function moveUp()
    local somethingUp, matchUp = upscan()
    if not somethingUp then
        turtle.up()
        return true
    else
        return false
    end
end


function moveForward()
    local somethingDown, somethingForward, matchDown, matchForward = innerscan()
    if not somethingForward then
        turtle.forward()
        return true
    else
        return false
    end
end

function moveLeft()
    turtle.turnLeft()
    return moveForward()
end

function moveRight()
    turtle.turnRight()
    return moveForward()
end

function moveBackTrack()
    turtle.turnRight()
    turtle.turnRight()
    moveForward()
    turtle.turnLeft()
    turtle.turnLeft()
end

local lastSide="left"

function run()
    if state == "toGround" then
        if not moveDown() then
            state = "scan"
        end
    elseif state == "backTrack" then
        state = "scanLeft-Right"
    elseif state == "scanLeft-Right" then
        if lastSide == "right" then
            lastSide="left"
            if moveLeft() then
                local somethingDown, somethingForward, matchDown, matchForward = innerscan()
                if matchDown then
                    -- right path!
                    state = "forwardAndScan"
                else
                    -- wrong path, double back

                    moveBackTrack()
                    turtle.turnRight()
                end
            else
                turtle.turnRight()
            end
        else
            lastSide="right"
            if moveRight() then
                local somethingDown, somethingForward, matchDown, matchForward = innerscan()
                if matchDown then
                    -- right path!
                    state = "forwardAndScan"
                else
                    moveBackTrack()
                    turtle.turnLeft()
                end
            else
                turtle.turnLeft()
            end
        end


    elseif state == "riseAndScan" then
        if moveUp() then
            if moveForward() then
                local somethingDown, somethingForward, matchDown, matchForward = innerscan()

                if matchDown then
                    -- one step up was a good assumption!
                    state = "forwardAndScan"
                else
                    state = "scanLeft-Right"
                end
            else
                state = "scanLeft-Right"
            end
        end
    elseif state == "forwardAndScan" then
        if moveForward() then
            local somethingDown, somethingForward, matchDown, matchForward = innerscan()
            if matchDown then
                -- right path, continue
                state = "forwardAndScan"
            else
                -- wrong path, is left or right
                moveBackTrack()
                state = "scanLeft-Right"
            end
        else
            state = "scanLeft-Right"
        end
    elseif state == "giveUp" then
        print("Giving up")
        return false
    elseif state == "scan" then
        scan()
    elseif state == "followLoop" then

    else
        state = "scan"
    end
    return true
end


while run() do
    -- nothing
    print("state: " .. state)
end

print("normal end")