A JSON or XML parsing library is certainly possible with procedural macros. I haven't had the pleasure of trying out Rust macros but if you are interested in ma

A JSON or XML parsing library is certainly possible with procedural macros. I haven't had the pleasure of trying out Rust macros but if you are interested in macros in general then I suggest taking a look at the Nimrod programming language (http://nimrod-lang.org http://nimrod-lang.org) as well as the talk on metaprogramming by the language's author: http://www.infoq.com/presentations/nimrod http://www.infoq.com/presentations/nimrod The Nimrod standard library has many examples of what macros can do. For example, I have been working on an async macro (now part of the latest Nimrod release) which allows asynchronous function calls to be made in a similar fashion to ordinary blocking function calls. It's very similar to C#'s await. The way it works is that it transforms functions marked as 'async' into an iterator, while at the same time transforming any occurrences of 'await' into a yield.