public RInternalResult Map(SymbolicExpression sexp)
        {
            //Comments return null instead of a SEXP.
            if (sexp == null) return new RInternalResult();

            var mapper = _mappers[sexp.Type];
            var mapped = mapper(sexp);

            var result = new RInternalResult
            {
                Type = sexp.Type.ToString(),
                Values = mapped.ToList()
            };

            return result;
        }
        public RInternalResult Map(SymbolicExpression sexp)
        {
            //Comments return null instead of a SEXP.
            if (sexp == null)
            {
                return(new RInternalResult());
            }

            var mapper = _mappers[sexp.Type];
            var mapped = mapper(sexp);

            var result = new RInternalResult
            {
                Type   = sexp.Type.ToString(),
                Values = mapped.ToList()
            };

            return(result);
        }