sS regexpFirstGroup(S pat, S s) {
  Matcher m = regexpMatcher(pat, s);
  if (m.find()) ret m.group(1); else null;
}

sS regexpFirstGroup(java.util.regex.Pattern pat, S s) {
  Matcher m = regexpMatcher(pat, s);
  if (m.find()) ret m.group(1); else null;
}

sS regexpFirstGroup(S pat, Iterable<S> strings) {
  var compiled = compileRegexp(pat);
  fOr (S s : strings)
    try object S group = regexpFirstGroup(compiled, s);
  null;
}