sbool printConceptGraph_showIDs;

static void printConceptGraph(Concept c) {

  printConceptGraph_impl(c, 0, "", new IdentityHashMap);

}

static void printConceptGraph_impl(Concept c, int indent, S prefix, IdentityHashMap seen) {

  bool isSeen = seen.containsKey(c);

  seen.put(c, c);

  StringBuilder buf = new StringBuilder;

  buf.append(prefix);

  S cname = dynamicShortName(c);

  if (eq(cname, "Str"))

    buf.append("Str " + quote(cget(c, "name")));

  else {

    buf.append(cname);

    if (printConceptGraph_showIDs)

      buf.append(" [" + c.id + (isSeen ? ", seen" : "") + "]");

    else if (isSeen)

      buf.append(" [seen]");

    for (S field : conceptFields(c)) {

      O val = cget(c, field);

      if (val != null && !val instanceof Concept)

        buf.append(" " + field + "=" + struct(val));

    }

  }

  printIndent(indent, buf);

  if (isSeen) ret;

  L<S> names = dynGetRefNames(c);

  for (S name : names) {

    Concept val = cast cget(c, name);

    if (eq(name, "_if")) name = "if"; // prettify

    printConceptGraph_impl(val, indent + 2, l(names) == 1 ? "" : name + "=", seen);

  }

}