// combines a value with the merged token range of two PWTs
static <A> ParsedWithTokens<A> pwt_combine(A value, ParsedWithTokens p1, ParsedWithTokens p2) {
  assertSame(p1.tok, p2.tok);
  ret new ParsedWithTokens(value, p1.tok, min(p1.iStart, p2.iStart), max(p1.iRemaining, p2.iRemaining));
}

// increases the token range of a PWT merging another PWT
static <A> ParsedWithTokens<A> pwt_combine(ParsedWithTokens<A> p1, ParsedWithTokens p2) {
  ret pwt_combine(p1!, p1, p2);
}

// Second meaning: Combines all parses pb out of a list B
//   with all parses pa out of a list A
//   where pb occurred to the right of pb.
//   (Also applies a user-defined combination function merging pa and pb into a new PWT value.)

static <A, B, C> L<ParsedWithTokens<C>> pwt_combine(Iterable<ParsedWithTokens<A>> l1, Iterable<ParsedWithTokens<B>> l2, IF2<A, B, C> f) {
  new L<ParsedWithTokens<C>> out;
  for (ParsedWithTokens<A> a : l1)
    for (ParsedWithTokens<B> b : pwt_toTheRightOf(l2, a))
      out.add(pwt_combine(f.get(a!, b!), a, b));
  ret out;
}

// Same thing with 3 lists.

static <A, B, C, D> L<ParsedWithTokens<D>> pwt_combine(Iterable<ParsedWithTokens<A>> l1, Iterable<ParsedWithTokens<B>> l2, Iterable<ParsedWithTokens<C>> l3, IF3<A, B, C, D> f) {
  new L<ParsedWithTokens<D>> out;
  for (ParsedWithTokens<A> a : l1)
    for (ParsedWithTokens<B> b : pwt_toTheRightOf(l2, a))
      for (ParsedWithTokens<C> c : pwt_toTheRightOf(l3, b))
        out.add(pwt_combine(f.get(a!, b!, c!), a, c));
  ret out;
}