Macro: SWITCH

Documentation

Evaluate the first clause whose car satisfies (funcall test car obj).

Source

(defmacro switch ((obj &key (test #'eql)) &body clauses)
  "Evaluate the first clause whose car satisfies (funcall test
  car obj)."
  ;; NB: There is no need to do the find-if and the remove here, we
  ;; can just as well do them with in the expansion
  (let ((default-clause (find-if (lambda (c) (eq t (car c))) clauses)))
    (when default-clause
      (setf clauses (remove default-clause clauses :test #'equalp)))
    (let ((obj-sym (gensym))
          (test-sym (gensym)))
      `(let ((,obj-sym ,obj)
             (,test-sym ,test))
         (cond
           ,@(mapcar (lambda (clause)
                       (let ((keys (ensure-list (car clause)))
                             (form (cdr clause)))
                         `((or ,@(mapcar (lambda (key)
					   `(funcall ,test-sym ',key ,obj-sym))
					 keys))
			   ,@form)))
                     clauses)
           ,@(when default-clause
                   `((t ,@(cdr default-clause)))))))))