;;
;; FILE:     list-functions.rkt
;; AUTHOR:   Eugene Wallingford
;; DATE:     2024/02/12
;; COMMENT:  Recursive functions for processing lists that are defined
;;           in class during Session 9.
;;

#lang racket
(require rackunit)

;; --------------------------------------------------------------------

(define (list-length lon)
  (if (null? lon)
      0
      (+ 1 (list-length (rest lon)))))     ; can use add1 here

;; --------------------------------------------------------------------
;; bonus function: so similar to any-bigger-than? !

(define (list-member? n lon)
  (if (null? lon)
      #f
      (or (= n (first lon))
          (list-member? n (rest lon)))))

;; --------------------------------------------------------------------

(define (remove-upto s los)
  (if (null? los)
      '()
      (if (eq? (first los) s)
          los
          (remove-upto s (rest los)))))

(check-equal? (remove-upto 'a '(a b c)) '(a b c))
(check-equal? (remove-upto 'b '(a b c)) '(b c))
(check-equal? (remove-upto 'd '(a b c)) '())
(check-equal? (remove-upto 'a '())      '())
(check-equal? (remove-upto 'a '(b d f g a a a a a a))
              '(a a a a a a))

;; --------------------------------------------------------------------

(define (remove-first s los)
  (if (null? los)
      '()
      (if (eq? (first los) s)
          (rest los)
          (cons (first los)
                (remove-first s (rest los))))))

(check-equal? (remove-first 'a '(a b c)) '(b c))
(check-equal? (remove-first 'b '(a b c)) '(a c))
(check-equal? (remove-first 'd '(a b c)) '(a b c))
(check-equal? (remove-first 'a '())      '())
(check-equal? (remove-first 'a '(a a a a a a a a a a))
              '(a a a a a a a a a))

;; --------------------------------------------------------------------

(define (remove s los) 
  (if (null? los)
      '()
      (if (eq? (first los) s)
          (remove s (rest los))
          (cons (first los) 
                (remove s (rest los))))))

(check-equal? (remove 'a '(a b c))               '(b c))
(check-equal? (remove 'a '(a a a a a a a a a a)) '())

;; --------------------------------------------------------------------