In fact you can have case-sensitive Common Lisp packages that are completely backwards compatible with case-insensitive CL code by settings readtable-case to :i

In fact you can have case-sensitive Common Lisp packages that are completely backwards compatible with case-insensitive CL code by settings readtable-case to :invert[1], and this works without any problems for interfacing with external case-sensitive environments.[2] Allegro's modern mode is what you would get if you assume case sensitivity as a default, but portable Common Lisp can handle case sensitivity perfectly fine without breaking backwards compatibility. [1] https://oneofus.la/have-emacs-will-hack/2011-09-20-common-lisp-is-case-sensitive.html https://oneofus.la/have-emacs-will-hack/2011-09-20-common-li... [2] https://common-lisp.net/project/parenscript/reference.html#section-symbolconv https://common-lisp.net/project/parenscript/reference.html#s...