code: public static ExprDouble toExprDouble(Expression expr, Position start, Position end) {
  	if (expr instanceof Literal) {
  	    Double d = ((Literal) expr).getDouble(null);
  	    if (d != null) {
  		return expr.getFactory().createLitDouble(-d.doubleValue(), start, end);
  	    }
  	}
  	return new OpNegateNumber(expr, start, end);
      }
docs: Create a String expression from a Expression
  
  @param left
  @param right
  
  @return String expression
  @throws TemplateException