With regards to 405′s, you can override the HandleUnknownAction method on a controller. I’ve created a base controller, and in that method check to see if the action matches a known method that doesn’t exist (I use Index, Get, Put, Post, Delete method names as part of my routing). If it does, throw an exception resulting in a 405. If not it throws a 404 as normal.

It’s not very elegant, but works for my setup. A filter would be nicer (HandleError?), I’ll need to read up and step through some code to see if it’s possible.

“You cannot change the language at run-time.”

For most languages, this is true, however, as you mentioned Smalltalk, I’d like to point out: the compiler is written in Smalltalk, and is thus available for modification (like everything else that lives above the VM) at run time. It’s usually comprised of a Parser class and a Scanner class. While Smalltalk has a small amount of syntax in the way of a macro system, it’s worth pointing out that it’s still a pretty trivial grammar, and parsed with recursive descent.

One fun trick is to use an anonymous function to simultaneously change the grammar and rewrite all the source code in the system in one go; *poof* new object language:)

Lots of fun can be had with pulling down e.g., Squeak, as well as perhaps OMeta, and playing around with ideas for macro systems.

Great article all the same! I often find myself struggling to explain the difference between a hygienic macro and a C macro to people who are only familiar with the latter.