static <A> Channels<A> lambdaMapLike mapChannels(IF1<Int, A> f, int channels) {
  Channels<A> cc = new(channels);
  for c to channels:
    cc.set(c, f.get(c));
  ret cc;
}

static <A> Channels<A> lambdaMapLike mapChannels(int channels, IF1<Int, A> f) {
  ret mapChannels(f, channels);
}