smh
8/12/2015 12:03:00 AM
The answer have answered the original question well.
There remains the question why current implementations don't provide this functionality.
The first reason is that the ANS (2.1.4 Character Syntax Types) reserves the two square braces for use by user code. But of course user code or a user-enabled extension could define these reader macros, so that's not the important reason.
The real reason is that the mostly-MACLISP character assignments of CL date from a time before the era of powerful WYSIWYG editors, that can automatically handle indenting and bracket pairing. While usable Emacs interfaces certainly existed during the time of the X3J13 process, they hadn't yet overcome historical thinking.
So "smart" bracket closers are no longer very necessary or helpful.