static <A> L<A> filter_pcall(Iterable<A> c, O pred) {
  if (pred instanceof F1) ret filter_pcall(c, (F1<A, Bool>) pred);

  new L x;
  if (c != null) for (O o : c)
    if (isTrue(pcallF(pred, o)))
      x.add(o);
  ret x;
}

static L filter_pcall(O pred, Iterable c) {
  ret filter_pcall(c, pred);
}

static <A, B extends A> L filter_pcall(Iterable<B> c, F1<A, Bool> pred) {
  new L x;
  if (c != null) for (B o : c) pcall {
    if (pred.get(o).booleanValue())
      x.add(o);
  }
  ret x;
}

static <A, B extends A> L filter_pcall(F1<A, Bool> pred, Iterable<B> c) {
  ret filter_pcall(c, pred);
}

Began life as a copy of #1003524