@Override
  public Oql visit(Constant constant) {
    String oqlAsString;
    if (useBindVariables) {
      variables.add(constant.value());
      oqlAsString = "$" + variables.size();
    } else {
      oqlAsString = valueToString(constant.value());
    }

    return oql(oqlAsString);
  }
Used for operators with two arguments like {@code =}, {@code IN} etc.
criteria/geode/src/org/immutables/criteria/geode/GeodeQueryVisitor.java