Great idea. A suggestion: it may have taken a bit more code, but a powerful and idiomatic way in C# would have been to parse S-Experssions into LINQ expression

Great idea. A suggestion: it may have taken a bit more code, but a powerful and idiomatic way in C# would have been to parse S-Experssions into LINQ expression trees. That would have made parsing more involved but would have made the Eval function trivial.