lambda.lisp

(defun flatten (structure)
  (cond ((null structure) nil)
        ((atom structure) (list structure))
        (t (mapcan #'flatten structure))))
        

(defun g!-symbol-p (s)
  (and (symbolp s)
       (> (length (symbol-name s)) 2)
       (string= (symbol-name s)
                "G!"
                :start1 0
                :end1 2)))
                
                
(defmacro defmacro/g! (name args &rest body)
  (let ((syms (remove-duplicates (remove-if-not #'g!-symbol-p (flatten body)))))
    `(defmacro ,name ,args
       (let ,(mapcar (lambda (s) `(,s (gensym ,(subseq (symbol-name s) 2)))) syms)
         ,@body))))
         
         
(macroexpand-1 '(defmacro/g! nif (expr pos zero neg)
  `(let ((,g!result ,expr))
     (cond ((plusp ,g!result) ,pos)
           ((zerop ,g!result) ,zero)
           (t ,neg)))))         


;; output
(DEFMACRO NIF (EXPR POS ZERO NEG)
     (LET ()
       `(LET ((,G!RESULT ,EXPR))
          (COND ((PLUSP ,G!RESULT) ,POS) ((ZEROP ,G!RESULT) ,ZERO) (T ,NEG)))))