アナフォリックマクロです

acond.el

(require 'cl)

(defmacro aif (test then &optional else)
  (declare (indent 2))
  `(let ((it ,test))
     (if it 
         ,then
       ,else)))

(defmacro acond (&rest clauses)
  (labels ((rec (clauses)
                (if clauses
                    `(aif ,(first (first clauses))
                         (progn ,@(rest (first clauses)))
                       ,(rec (rest clauses)))
                  nil)))
    (rec clauses)))



;;;; 使用例
;; ハッシュテーブルにkey:takahashi value:35が登録してある状況で
(setf *hash* (make-hash-table))
(setf (gethash 'takahashi *hash*) 35)
 
(cond ((gethash 'yamada *hash*) (format "yamada's value was found: %s" (gethash 'yamada *hash*)))
      ((gethash 'takahashi *hash*) (format "takahashi's value was found: %s" (gethash 'takahashi *hash*))))
;=> "takahashi's value was found: 35"
; が
 
(acond ((gethash 'yamada *hash*) (format "yamada's value was found: %s" it))
       ((gethash 'takahashi *hash*) (format "takahashi's value was found: %s" it)))
;=> "takahashi's value was found: 35"
; と書けます