defineVisitor(writer, baseName, types);

        // The base accept() method.
        writer.println();
        writer.println("  abstract <R> R accept(Visitor<R> visitor);");

    private static void defineVisitor(
            PrintWriter writer, String baseName, List<String> types) {
        writer.println("  interface Visitor<R> {");

        for (String type : types) {
            String typeName = type.split(":")[0].trim();
            writer.println("    R visit" + typeName + baseName + "(" +
                    typeName + " " + baseName.toLowerCase() + ");");
        }
        writer.println("  }");
    }

        // Visitor pattern.
        writer.println();
        writer.println("    @Override");
        writer.println("    <R> R accept(Visitor<R> visitor) {");
        writer.println("      return visitor.visit" +
            className + baseName + "(this);");
        writer.println("    }");