public ParserScanner(TextReader reader, IMathSystem system)
        {
            if(system == null)
                throw new ArgumentNullException("system");
            if(reader == null)
                throw new ArgumentNullException("reader");

            tokenizer = new ParserMarker(reader);
            this.system = system;
            this.library = Service<ILibrary>.Instance;
            this.builder = Service<IBuilder>.Instance;
        }
        public ParserScanner(TextReader reader, IMathSystem system)
        {
            if (system == null)
            {
                throw new ArgumentNullException("system");
            }
            if (reader == null)
            {
                throw new ArgumentNullException("reader");
            }

            tokenizer    = new ParserMarker(reader);
            this.system  = system;
            this.library = Service <ILibrary> .Instance;
            this.builder = Service <IBuilder> .Instance;
        }