Instaparse
Instaparse aims to be the simplest way to build parsers in Clojure
...Instaparse supports most of the common notations for context-free grammars. For example, a popular alternative to * is to surround the term with curly braces {}, and a popular alternative to ? is to surround the term with square brackets []. Rules can be specified with =, :, :=, or ::=. Rules can optionally end with ;. Instaparse is very flexible in terms of how you use whitespace (as in Clojure, , is treated as whitespace) and you can liberally use parentheses for grouping.