62 lines
2.1 KiB
Racket
62 lines
2.1 KiB
Racket
#lang racket/base
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(require racket/local
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racket/list)
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;; A blog is a (blog home posts)
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;; where home is a string, posts is a (listof post)
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(struct blog (home posts) #:mutable #:prefab)
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;; and post is a (post blog title body comments)
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;; where title is a string, body is a string,
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;; and comments is a (listof string)
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(struct post (title body comments) #:mutable #:prefab)
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;; initialize-blog! : path? -> blog
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;; Reads a blog from a path, if not present, returns default
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(define (initialize-blog! home)
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(local [(define (log-missing-exn-handler exn)
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(blog
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(path->string home)
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(list (post "Second Post"
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"This is another post"
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(list))
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(post "First Post"
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"This is my first post"
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(list "First comment!")))))
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(define the-blog
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(with-handlers ([exn? log-missing-exn-handler])
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(with-input-from-file home read)))]
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(set-blog-home! the-blog (path->string home))
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the-blog))
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;; save-blog! : blog -> void
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;; Saves the contents of a blog to its home
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(define (save-blog! a-blog)
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(local [(define (write-to-blog)
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(write a-blog))]
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(with-output-to-file (blog-home a-blog)
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write-to-blog
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#:exists 'replace)))
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;; blog-insert-post!: blog string string -> void
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;; Consumes a blog and a post, adds the post at the top of the blog.
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(define (blog-insert-post! a-blog title body)
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(set-blog-posts!
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a-blog
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(cons (post title body empty) (blog-posts a-blog)))
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(save-blog! a-blog))
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;; post-insert-comment!: blog post string -> void
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;; Consumes a blog, a post and a comment string. As a side-efect,
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;; adds the comment to the bottom of the post's list of comments.
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(define (post-insert-comment! a-blog a-post a-comment)
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(set-post-comments!
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a-post
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(append (post-comments a-post) (list a-comment)))
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(save-blog! a-blog))
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(provide blog? blog-posts
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post? post-title post-body post-comments
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initialize-blog!
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blog-insert-post! post-insert-comment!)
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