sS regexpReplace_direct(S s, S pat, S replacement) {
  Matcher m = regexp(pat, s);
  ret regexpReplace_direct(m, replacement);
}
  
sS regexpReplace_direct(Matcher m, S replacement) {
  new StringBuffer buf;
  while (m.find())
    m.appendReplacement(buf, replacement);
  m.appendTail(buf);
  ret str(buf);
}