!759

answer {
  if (!attn()) ret null;
  
  s = s.trim();
  if (s.startsWith("eval ")) exceptionToUser {
    s = dropPrefix("eval ", s);
    Lisp l = nlParse(s);
    new EvalTransform e;
    Lisp t = e.evalTransformRule(l);
    if (e.exception != null) printStackTrace(e.exception);
    ret nlUnparse(t) + (e.exception == null ? "" : "\n" + e.exception);
  }
}