defvariant

Variants for Common Lisp (for ML nostalgics ?)

(defpackage :try-defvariant
  (:use :cl :defvariant))

(in-package :try-defvariant)

(defvariant btree
   (leaf)
   (node val left right))

=> MATCH-BTREE

(let ((my-tree
        (make-btree-node :val 42 
                         :left (make-btree-leaf) 
                         :right (make-btree-leaf))))
  (match-btree my-tree
        (leaf _ "leaf !")
        (node (v _ _) v)))

=> 42

See. defvariant.md for the whole story.