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Fixing PR12881

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Jay McCarthy 2012-07-10 19:21:15 -04:00
parent 1685952b9b
commit a7ea79040d
1 changed files with 17 additions and 14 deletions
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31
collects/web-server/scribblings/tutorial/continue.scrbl
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@ -468,20 +468,23 @@ in a new browser window. What happens when you try this?
@section{Share and Share Alike}
@declare-exporting[#:use-sources (web-server/scribblings/tutorial/examples/iteration-4)]
The problem with our application is that each browser
window keeps track of its own distinct blog. For most people, this defeats
the purpose of a blog, which is to share with others! When we insert a
new post, rather than creating a new blog value, we'd like to make a
structural change to the existing
blog. (@italic{@link["http://www.htdp.org/"]{How to Design Programs}},
Chapter 41). So let's add mutation to the mix.
The problem with our application is that each browser window keeps
track of its own distinct blog. For most people, this defeats the
purpose of a blog, which is to share with others! When we insert a
new post, rather than creating a new blog value, we'd like to modify
@emph{the} blog. In other words, we'd like to make a structural
change. (@italic{@link["http://www.htdp.org/"]{How to Design
Programs}}, Chapter 41). So let's switch from just the @racket[BLOG]
binding to a list and instead bind it to a mutable structure. If we
were to just use a structure, we'd write the following:
There's one small detail we need to touch on: by default, structures in the
@racket[web-server] language are immutable. To gain access to structure
mutators, we'll need to override this default, by adding the @racket[#:mutable]
keyword to some of our structure definitions. In particular, if we want to
allow changes to a blog, we must change our definition of the blog structure to
the following:
@racketblock[(struct blog (posts))]
But, by default, structures in Racket are immutable. To gain access
to structure mutators, we'll need to override this default, by adding
the @racket[#:mutable] keyword to some of our structure
definitions. In particular, if we want to allow changes to a blog, we
must change our definition of the blog structure to the following:
@racketblock[(struct blog (posts) #:mutable)]
@ -499,7 +502,7 @@ which allows us to change the posts of a blog:
@defthing[blog-insert-post! (blog? post? . -> . void)]
whose intended side effect is to extend a blog's post.
whose intended side effect is to extend a blog's posts.
@centerline{------------}