static bool ctxEvalPattern(S pat) {
  if (empty(pat)) true;
  CtxContext c = ctxContext();
  WoodyBot bot = woodyBot();
  Pattern p;
  if (bot != null)
    p = bot.compiledPatterns.get(pat);
  if (p == null) {
    pat = ctxExpandMacros(pat, c.regexpMacros);
    S re = ctxREToJavaRE(pat);
    p = Pattern.compile(re, Pattern.CASE_INSENSITIVE);
  }
  if (bot != null)
    bot.compiledPatterns.put(pat, p);
  ret p.matcher(c.input).find();
}