;; This file contains excerpts from the textbook Concrete
;; Abstractions: An Introduction to Computer Science Using Scheme, by
;; Max Hailperin, Barbara Kaiser, and Karl Knight, Copyright (c) 1998
;; by Brooks/Cole Publishing Company. This file may not be reproduced
;; or redistributed other than for use with that textbook.

;; Chapter 7: Lists

;; 7.3  Basic List Processing Techniques

(define filter
  (lambda (ok? lst)
    (cond ((null? lst)
           '())
          ((ok? (car lst))
           (cons (car lst) (filter ok? (cdr lst))))
          (else
           (filter ok? (cdr lst))))))

;; Chapter 14: Object-Oriented Programming

;; 14.5  An Application: Adventures in the Imaginary Land of Gack

(define delq
  (lambda (item list)
    (filter (lambda (x)
              (not (eq? x item)))
            list)))

(define display-message
  (lambda (list-of-stuff)
    (newline)
    (for-each (lambda (s) (display s) (display " "))
              list-of-stuff)))

(define verbalize-list
  (lambda (items none-word)
    (define loop
      (lambda (items)
        (if (null? (cdr items))
            items
            (cons (car items)
                  (cons "and"
                        (loop (cdr items)))))))
    (if (null? items)
        (list none-word)
        (loop items))))

(define random-element
  (lambda (list)
    (if (null? list)
        #f
        (list-ref list (random (length list))))))

;; THIS IS A PROCEDURE ADDED BY DAVID WOLFE IN FALL 2001 WHICH
;; ATTEMPTS TO BE A BIT MORE INFORMATIVE THAN oops-display.

(define oops-describe
  (lambda (x)
    (define MAX_LIST_LENGTH 15)
    (define display-each
      (lambda (lst)
	(for-each display lst)))
    (define display-list
      (lambda (lst)
        (define do-it
          (lambda (lst max-list-length)
            (cond ((null? lst))
                  ((= max-list-length 0) (display "..."))
                  ((= (length lst) 1) (oops-display (car lst)))
                  (else (oops-display (car lst))
                        (display " ")
                        (do-it (cdr lst) (- max-list-length 1))))))
        (do-it lst MAX_LIST_LENGTH)))
    (define describe-verbose
      (lambda (x)
	(cond ;((object? x) (object/describe x))
         ((vector? x)
          (display "#")
          (describe-verbose (vector->list x)))
         ((or (string? x) (number? x) (symbol? x) (boolean? x))
          (write x))
         ((list? x)
          (display "(")
          (display-list x)
          (display ")"))
         ((procedure? x) (display "<Procedure>"))
         ((pair? x)
          (display "(")
          (oops-display (car x))
          (display " . ")
          (oops-display (cdr x))
          (display ")"))
         (else (display-each (list "<UnrecognizedByDescribe:" x ">"))))))
    (describe-verbose x)))