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));
}