Beyond Traditional Pattern Matching in Lisp

Summary

Exploring LispE: A Distinctive Take on Lisp Through Pattern Matching and Logic LispE, a modern Lisp dialect developed by Naver, introduces innovative constructs— defpat , defmacro , and defpred —that set it apart from traditional Lisp implementations like Common Lisp, Scheme, and Clojure. While Lisp dialects share a heritage of flexibility and macro systems, LispE extends this with advanced pattern matching, enhanced macro capabilities, and logic programming elements. This blog entry examines these features, comparing them to their counterparts in other Lisps with specific examples to highlight LispE’s unique approach. defpat : Pattern Matching in Function Definitions LispE’s defpat enables defining multiple functions under the same name, each triggered by a specific argument pattern. This offers a declarative way to handle polymorphism beyond type-based dispatching. LispE Example 1 (FizzBuzz): ( defun checkmod (v d) ( eq (% v d) 0 )) (defpat fizzbuzz ([integer_ (checkmod x 15 )]) ' fizzbuzz) (defpat fizzbuzz ([integer_ (checkmod x 3 )]) ' fizz) (defpat fizzbuzz ([integer_ (checkmod x 5 )]) ' buzz) (defpat fizzbuzz (x) x) ( mapcar ' fizzbuzz (range 1 15 1 )) Output: (1 2 fizz 4 buzz fizz 7 8 fizz buzz 11 fizz 13 14 fizzbuzz) . The nested patterns (e.g., (integer_ (checkmod x 3)) ) match integers divisible by 3, with a fallback for unmatched cases. LispE Example 2 (Kleene Operator): To further illustrate defpat ’s capabilities, consider its support for Kleene operators ( + , * , % ), which allow matching sequences of arguments. a% : means that the element is optional a* : means that this element can be present 0 or n times a+ : means that this element should be present at least once Here’s an example that processes a list of numbers, collecting those less than 10: (defpat collect-small ([( < x 10 )+ $ rest]) (println " Collected: " x " Remaining: " rest ) x ) (defpat collect-small (lst) (println " No small numbers in: " lst) ' () ) (collect-small ' ( 5 8 12 3 15 )) O...