In Common Lisp, the library CL-PPCRE [0] is used for regexes, and has an "AST"-syntax like this. It supports full Perl-compatible regular expressions in both th

In Common Lisp, the library CL-PPCRE [0] is used for regexes, and has an "AST"-syntax like this. It supports full Perl-compatible regular expressions in both the tree syntax as well as the standard string syntax. The tree syntax actually uses symbols and lists, idiomatic in symbolic programming settings. This has the hugely convenient property of being trivially serializable, just as the string representation is. This isn't true with an unadorned object representation. The documentation for the tree syntax is here [1]. Some examples from the page are reproduced below. The PARSE-STRING function isn't used by the user except for testing. All of the regex scanning and matching functions allow either a string or a tree. * (parse-string "(ab)*") (:GREEDY-REPETITION 0 NIL (:REGISTER "ab")) * (parse-string "(a(b))") (:REGISTER (:SEQUENCE #\a (:REGISTER #\b))) * (parse-string "(?:abc){3,5}") (:GREEDY-REPETITION 3 5 (:GROUP "abc")) ;; (:GREEDY-REPETITION 3 5 "abc") would also be OK * (parse-string "a(?i)b(?-i)c") (:SEQUENCE #\a (:SEQUENCE (:FLAGS :CASE-INSENSITIVE-P) (:SEQUENCE #\b (:SEQUENCE (:FLAGS :CASE-SENSITIVE-P) #\c)))) ;; same as (:SEQUENCE #\a :CASE-INSENSITIVE-P #\b :CASE-SENSITIVE-P #\c) * (parse-string "(?=a)b") (:SEQUENCE (:POSITIVE-LOOKAHEAD #\a) #\b) [0] http://weitz.de/cl-ppcre/ http://weitz.de/cl-ppcre/ [1] http://weitz.de/cl-ppcre/#create-scanner2 http://weitz.de/cl-ppcre/#create-scanner2