#lang scheme

;; A blog is a (make-blog posts)
;; where posts is a (listof post)
(define-struct blog (posts) #:mutable)

;; and post is a (make-post title body comments)
;; where title is a string, body is a string, 
;; and comments is a (listof string)
(define-struct post (title body comments) #:mutable)

;; BLOG: blog
;; The initial BLOG.
(define BLOG 
  (make-blog
   (list (make-post "First Post" 
                    "This is my first post" 
                    (list "First comment!"))
         (make-post "Second Post" 
                    "This is another post"
                               (list)))))

;; blog-insert-post!: blog post -> void
;; Consumes a blog and a post, adds the post at the top of the blog.
(define (blog-insert-post! a-blog a-post)
  (set-blog-posts! 
   a-blog
   (cons a-post (blog-posts a-blog))))

;; post-insert-comment!: post string -> void
;; Consumes a post and a comment string.  As a side-efect, 
;; adds the comment to the bottom of the post's list of comments.
(define (post-insert-comment! a-post a-comment)
  (set-post-comments!
   a-post
   (append (post-comments a-post) (list a-comment))))

(provide (all-defined-out))