#lang racket
(define add-generator
  (lambda (n)
    (lambda (m)
      (+ n m))))

(define add42 (add-generator 42))
(define add7 (add-generator 7))

(define make-list-cleaner
  (lambda (item)
    (lambda (ls)
      (filter (lambda (x) (not (eq? item x))) ls))))

(define remove-zeros (make-list-cleaner 0))
; (remove-zeros '(1 2 0 0 3 0 5)) => '(1 2 3 5)
(define remove-qs (make-list-cleaner 'q))
; (remove-qs '(1 2 q a d f)) => '(1 2 a d f)

(define make-limited
  (lambda (proc)
    (lambda ls
      (if (> (length ls) 3)
          'unreasonable
          (apply proc ls)))))

(define limited+ (make-limited +))
; (limited+ 1 2) => 3
; (limited+ 10 20 30) => 60
; (limited+ 3 4 5 6) => 'unreasonable
; up to three arguments is fine