var i = 0;
var state = true;
var inc = 1
while(true)
{
    delay(500) // wait 500ms
    if(++i < nbLeds and i >= 0) // i between 0 and max led
    {
        switch(Led[i], state);
        i = i + inc;
    }
    else if( i > 0) // i higher than max led
    {
        inc = (-1)*inc; // invert increment
        state = !state; // invert state
    }
    else // i is < 0
    {
        inc = (-1)*inc; // invert increment
        state = !state; // invert state
    }
}