txt = "Hello, world! "
left = True

def draw():
    global txt
    background(128)
    text(txt, 10, height / 2)
    if frameCount % 10 == 0:
        if (left):
            txt = rotate(txt, 1)
        else:
            txt = rotate(txt, -1)
        println(txt)

def mouseReleased():
    global left
    left = not left

def rotate(text, startIdx):
    rotated = text[startIdx:] + text[:startIdx]
    return rotated