AV *frobnicate(AV *foo)
  INIT:
    int i;

  CODE:
    RETVAL = newAV();
    sv_2mortal((SV *)RETVAL);

    for (i = 0; i < av_len(foo); i += 2) {
      SV **cell = av_fetch(foo, i, 0);
      if (cell && *cell)
        av_push(RETVAL, SvREFCNT_inc(*cell));
    }

  OUTPUT:
    RETVAL