towers of hanoi | Takeuchi function | combinations of a set | letrec macro
;;; Scheme's LETREC and LETREC*
(defmacro letrec (bs x . xs)
(let ((vs (mapcar car bs))
(as (mapcar cadr bs))
(gs (mapcar (lambda (x) (gensym)) bs)))
(let ((ns (mapcar (lambda (x) @(,x nil)) vs))
(is (mapcar (lambda (v g) @(setq ,v ,g))
vs gs)))
@(let (,@ns) ((lambda ,gs ,@is ,x . ,xs) . ,as)))))
(defmacro letrec* (bs x . xs)
(let ((vs (mapcar car bs))
(as (mapcar cadr bs))
(ns (mapcar (lambda (x) nil) bs)))
(let ((is (mapcar (lambda (v a) @(setq ,v ,a))
vs as)))
@((lambda ,vs ,@is ,x . ,xs) . ,ns))))