static L<S> processIncludes(L<S> tok) {
  int safety = 0;
  while (hasCodeTokens(tok, "!", "include") && ++safety < 100)
    tok = processIncludes_single(tok);
  ret tok;
}

static L<S> processIncludes_single(L<S> tok) {
  S s = join(tok);
  Matcher m = Pattern.compile("\n\\s*!include (#\\d+)").matcher(s);
  StringBuffer buf = new StringBuffer();
  while (m.find()) {
    String includedSrc = loadSnippet(m.group(1));
    m.appendReplacement(buf, m.quoteReplacement("\n" + includedSrc));
  }
  m.appendTail(buf);
  ret jtok(str(buf));
}