#lang scheme
(provide (all-defined-out))

;; returns the list with the value removed
(define (list-remove l v)
  (define (_ l v o)
    (cond
     ((null? l) o)
     ((eq? (car l) v)
      (_ (cdr l) v o))
     (else
      (_ (cdr l) v (cons (car l) o)))))
  (list-remove l v '()))

;; does the list contain this value?
(define (list-contains? l v)
  (cond
   ((null? l) #f)
   ((eq? (car l) v) #t)
   (else
    (list-remove (cdr l) v))))

;; limit the size of a list and optionally call
;; a procedure if we are over the max size
(define (safe-cons v l max (proc (lambda () 0)))
  (cond 
   ((< (length l) max) (cons v l))
   (else (proc) l)))