But if you really like this syntax, there is nothing in the ANS that would preclude a source module from including the necessary read-time set-dispatch-macro-char call early in its own source.
Module-local syntax would be nice, but there is currently no editor(Emacs) and ASDF support for that so I won't use it
1- Since ASDF 2.019, there is support for :around-compile, that allows you to effectively redefine syntax around a module. Combined with reader-interception, you can portably redefine your syntax to be that of e.g. python, or whatever you fancy. You know where to find emacs modes.
2- Since well before that, there is named-readtables. I recommend you make your #; syntax available as a named readtable.
3- You can always define a new subclass of cl-source-file, that gets compiled within proper syntax redefinition.
—♯ƒ • François-René ÐVB Rideau •Reflection&Cybernethics• http://fare.tunes.org Two wrongs don't make a right — but three lefts do.