Colin Shivers with a discussion about the usual 80% solutions versus the benefit of a 100% solution, followed by his 100% solution of regexes represented by S-expressions for scsh (using Henry Spencer...
Also check out the Common Lisp Portable Perl Compatible Regular Expression library.
https://edicl.github.io/cl-ppcre/#create-scanner2
https://edicl.github.io/cl-ppcre/#create-scanner2