static String structure(Object o) {
  return structure(o, 0);
}

// leave to false, unless unstructure() breaks
static boolean structure_allowShortening = false;
  
static String structure(Object o, int stringSizeLimit) {
  if (o == null) return "null";
  String name = o.getClass().getName();
  
  new StringBuilder buf;
  
  if (o instanceof Collection) {
    for (Object x : (Collection) o) {
      if (buf.length() != 0) buf.append(", ");
      buf.append(structure(x, stringSizeLimit));
    }
    return "[" + buf + "]";
  }
  
  if (o instanceof Map) {
    for (Object e : ((Map) o).entrySet()) {
      if (buf.length() != 0) buf.append(", ");
      buf.append(structure(((Map.Entry) e).getKey(), stringSizeLimit));
      buf.append("=");
      buf.append(structure(((Map.Entry) e).getValue(), stringSizeLimit));
    }
    return "{" + buf + "}";
  }
  
  if (o.getClass().isArray()) {
    int n = Array.getLength(o);
    for (int i = 0; i < n; i++) {
      if (buf.length() != 0) buf.append(", ");
      buf.append(structure(Array.get(o, i), stringSizeLimit));
    }
    return "{" + buf + "}";
  }

  if (o instanceof String)
    return quote(stringSizeLimit != 0 ? shorten((String) o, stringSizeLimit) : (String) o);
  
  // Need more cases? This should cover all library classes...
  if (name.startsWith("java.") || name.startsWith("javax."))
    return String.valueOf(o);
    
  String shortName = o.getClass().getName().replaceAll("^main\\$", "");

  // TODO: go to superclasses too
  Field[] fields = o.getClass().getDeclaredFields();
  int numFields = 0;
  String fieldName = "";
  for (Field field : fields) {
    if ((field.getModifiers() & Modifier.STATIC) != 0)
      continue;
    Object value;
    try {
      field.setAccessible(true);
      value = field.get(o);
    } catch (Exception e) {
      value = "?";
    }
    
    fieldName = field.getName();
    
    // put special cases here...

    if (value != null) {
      if (buf.length() != 0) buf.append(", ");
      buf.append(fieldName + "=" + structure(value, stringSizeLimit));
    }
    ++numFields;
  }
  String b = buf.toString();
  
  if (numFields == 1 && structure_allowShortening)
    b = b.replaceAll("^" + fieldName + "=", ""); // drop field name if only one
  String s = shortName;
  if (buf.length() != 0)
    s += "(" + b + ")";
  return s;
}