A selector is an object -- so that is pure -- and its use is a convention of the messaging, and the message itself is one object, that is an instance of Class message.
What's fun is that every Smalltalk contained the tools to make their successors while still running themselves. In other words, we can modify pretty much anything in Smalltalk on the fly if we choose to dip into the "meta" parts of it, which are also running. In Smalltalk-72, a message send was just a "notify" to the receiver that there was a message, plus a reference to the whole message. The receiver did the actual work of looking at it, interpreting it, etc.
This is quite possible to make happen in the more modern Smalltalks, and would even be an interesting exercise for deep Smalltalkers.
What's fun is that every Smalltalk contained the tools to make their successors while still running themselves. In other words, we can modify pretty much anything in Smalltalk on the fly if we choose to dip into the "meta" parts of it, which are also running. In Smalltalk-72, a message send was just a "notify" to the receiver that there was a message, plus a reference to the whole message. The receiver did the actual work of looking at it, interpreting it, etc.
This is quite possible to make happen in the more modern Smalltalks, and would even be an interesting exercise for deep Smalltalkers.