(defun remove-if (pred lis)
  (label ((ri (lambda (pred lis into)
                (cond
                 ((null lis) (nreverse into))
                 ((pred (car lis)) (ri pred (cdr lis) into))
                 (true (ri pred (cdr lis) (cons (car lis) into)))))))
         (ri pred lis nil)))
(macro dolist
  (lambda (args)
    `(progn
       (mapcar (lambda (,(caar args)) ,@(cdr args))
               ,(cadar args))
       nil)))

(defun take-while (pred lis) (car (split-at-first pred lis)))
(defun drop-until (pred lis) (cadr (split-at-first pred lis)))

;; (take-and-drop 3 '(1 2 3 4 5 6)) => ((1 2 3) (4 5 6))
(defun take-and-drop (n l)
  (label ((sazbi
           (lambda (n l one)
             (cond
              ((<= n 0) (list (nreverse one) l))
              (true (sazbi (- n 1) (cdr l) (cons (car l) one)))))))
         (sazbi n l nil)))
(defun take (n l) (car (take-and-drop n l)))
(defun drop (n l) (cadr (take-and-drop n l)))
(defun repeated (n v)
  (cond
   ((<= n 0) nil)
   (true (cons v (repeated (- n 1) v)))))
(defun left-pad-to (n v l)
  (let ((lacking (- n (list-length l))))
    (cond ((<= lacking 0) l)
          (true (append (repeated lacking v) l)))))
;; example: (setq xs '(1 2 3 4 5))
;;          (multilet ((a b c d e) xs) c) => 3
;; you can only multilet one list of variables at once.
(macro multilet
  (lambda (args)
    (cond
     ((atom (car args)) (error "multilet without enough parentheses"))
     ((atom (caar args)) (error "multilet without enough parentheses"))
     (true
      (label ((names (caar args))
              (value-list (cadar args)))
             `(apply (lambda ,names ,@(cdr args)) ,value-list))))))
;; example: (setq ns '(a b c d e))
;;          (setq xs '((1 2 3 4 5) (6 7 8 9 10)))
;;          (do-table (ns xs)
;;             (print c))
;; => 3
;;    8
;;    ()
(macro do-table
  (lambda (args)
    `(dolist (vlan ,(cadar args))
       (multilet (,(eval (caar args)) vlan)
                 ,@(cdr args)))))
;; elisp:
;; (put 'multilet 'lisp-indent-function 1)
;; (put 'do-table 'lisp-indent-function 1)