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);
  }
}