Updated README and cabal file for hakyll-0.2.
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Jasper Van der Jeugt
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README.markdown
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README.markdown
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@ -1,8 +1,8 @@
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# Hakyll
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# Hayll
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Hakyll is a simple static site generator library in Haskell. It is mostly
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inspired by [Jekyll](http://github.com/mojombo/jekyll), but I like to believe
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it is simpler. An example site where it is used is
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inspired by [Jekyll](http://github.com/mojombo/jekyll), but I like to
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believe it is simpler. An example site where it is used is
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[my personal homepage](http://jaspervdj.be) of which
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[the source code](http://jaspervdj.be/snapshot.tar.gz) is available as a
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reference.
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@ -19,6 +19,7 @@ be generated. In the rest of this document, we will examine a small example.
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This is our directory layout:
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|-- _cache
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|-- _site
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|-- favicon.ico
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|-- hakyll.hs
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@ -29,12 +30,16 @@ This is our directory layout:
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| `-- sample.html
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`-- text.markdown
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The `_cache` and `_site` directories will be automatically created by hakyll.
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## Static files
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Static files can be rendered using the `static` command. This command ensures
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the files will copied when you compile the site.
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Static files can be rendered using the `static` function. This function
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ensures the files will copied when you compile the site. Hakyll is smart enough
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to know when files have changed, and will check the modification time of a file
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before copying.
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For convenience reasons, there is also a `staticDirectory` command, which works
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For convenience reasons, there is also a `staticDirectory` function, which works
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recursively.
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main = do
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@ -44,9 +49,8 @@ recursively.
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## Pages
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Pages can be written in html, markdown, LaTeX, and basically anything
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pandoc supports. They can also contain metadata, which are always key-value
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mappings.
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Pages can be written in html, markdown, LaTeX, and basically anything pandoc
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supports. They can also contain metadata, which are always key-value mappings.
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---
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author: Jasper Van der Jeugt
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@ -61,11 +65,11 @@ mappings.
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main = putStrLn "Hello World!"
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~~~~
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Metadata is always placed in the beginning of a file, and is delimited by a
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`---` string. The metadata can only contain simple key-value pairs. We can
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now read in this page using the `Text.Hakyll.Page.readPage` function. This
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will return a `Page`, which is actually just a `Map String ByteString`. In
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this example, the map would consist of the following key-value pairs:
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Metadata is always placed in the header of a file, and is delimited by a `---`
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string. The metadata can only contain simple key-value pairs. We can now read
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in this page using the `Text.Hakyll.Page.readPage` function. This will return a
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`Page`, which is actually just a `Map String ByteString`. In this example, the
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map would consist of the following key-value pairs:
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- `author`: `Jasper Van der Jeugt`
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- `title`: `A sample markdown post`
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@ -79,7 +83,7 @@ In hakyll, there is a strict separation between pages and templates. Templates,
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for example, cannot contain metadata.
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<h2> $title </h2>
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by <strong> $author </title>
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by <strong> $author </strong>
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$body
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@ -87,16 +91,18 @@ Templates are rendered using the Haskell `Text.Template` library. This means
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that in your template, you can use `$identifier`, and it will be replaced by
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the value of `identifier`.
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With this template we could, for example, render the file we saw in the previous
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section. It would go like this:
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With this template we could, for example, render the file we saw in the
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previous section. It would go like this:
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page <- readPage "text.markdown"
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render <- renderPage "templates/sample.html" page
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Now, `render` will be a `Page` containing all metadata from `page`, but the
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`body` key would be replaced by the substitution. This means we can combine
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rendering actions. Given another template `templates/default.html`:
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rendered <- render "templates/sample.html" page
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writePage rendered
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This reads in `text.markdown`, renders it and writes it to the site destination
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(`_site/text.html`). The result of a `render` action is an `IO Page`, the
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metadata will be copied from the original page, and the body will be replaced by
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the rendering result. This means we can combine rendering actions. Given another
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template `templates/default.html`:
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<html>
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<head>
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<title> $title </title>
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@ -106,29 +112,39 @@ rendering actions. Given another template `templates/default.html`:
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</body>
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</html>
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We can now combine the rendering actions:
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page <- readPage "text.markdown"
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render <- (renderPage "templates/sample.html" page >>=
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renderPage "templates/default.html")
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Of course, you can't really do anything with the render if you don't write it
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to a file somewhere. That's why the function `renderAndWrite` exists:
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We can now combine the rendering actions (I use `>>=` notation here):
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readPage "text.markdown" >>=
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renderPage "templates/sample.html" page >>=
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renderAndWrite "templates/default.html"
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render "templates/sample.html" >>=
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render "templates/default.html" >>=
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writePage
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Now, where will this file be written? In `_site/text.html`, of course! That's
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because the page still contains a key called `url`, which the renderAndWrite
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function uses to determine the file destination.
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Jolly good fun and all that, but you can imagine that when we render over nine
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thousand posts, our generator will be busy for a while. That's why we have the
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`depends` function. It takes a url and a list of dependencies as arguments, and
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an IO action. The trick is that this IO action will only be executed if any of
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the dependencies is newer than the url given. In our example, we would write:
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depends "text.html" ["text.markdown", "templates/sample.html", "templates/default.html"]
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(readPage "text.markdown" >>= render "templates/sample.html" >>=
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render "templates/default.html" >>= writePage)
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Not exactly the prettiest code I've ever seen. Because rendering a page with a
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number of templates is very common, there's a `renderChain` function to do this
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for us. The above can be replaced by
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renderChain ["templates/sample.html", "templates/default.html"] $
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createPagePath "text.markdown"
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The `renderChain` function will automatically check dependencies and write the
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page. In fact, it is recommended that you __always__ use this, even when there's
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only one template in the chain.
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## More advanced things
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Sometimes, you want to create a `Page` from scratch, without reading from a
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file. There are functions to do that for you, and I suggest you read the
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documentation of `Text.Hakyll.Page`. As a more advanced example, I will
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explain the RSS system I wrote for my website.
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documentation of `Text.Hakyll.Page`. As a more advanced example, I will explain
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the RSS system I wrote for my website.
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|-- generate.hs
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|-- posts
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@ -137,24 +153,25 @@ explain the RSS system I wrote for my website.
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|-- rss.xml
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`-- rssitem.xml
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Our post contains some metadata:
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Our post contains some metadata:</p
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---
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title: A first post
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date: December 2, 2009
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about: A post describing the why and the how of the technical setup of this blog.
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---
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# A first post
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A first post describing the technical setup of this blog, for that is
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The `templates/rssitem.xml` file is a template for rendering one post to an
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rss item:
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The `templates/rssitem.xml` file is a template for rendering one post to an rss
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item:
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<item>
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<title> $title </title>
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<link>http://jaspervdj.be/$url</link>
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<description>New blogpost: $title</description>
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<description> $about </description>
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</item>
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Now a template for rendering the whole rss feed, `templates/rss.xml`:
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@ -169,16 +186,39 @@ Now a template for rendering the whole rss feed, `templates/rss.xml`:
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</channel>
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</rss>
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Alright, let's get coding.
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Alright, let's get coding. We first want a list of all posts, sorted so the most
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recent entries are first in the list.
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-- Find all posts paths.
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postPaths <- liftM (L.reverse . L.sort) $ getRecursiveContents "posts"
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-- Read and render all posts with the rssitem.xml template
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-- Also, only render 5 posts.
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pages <- mapM readPage (take 5 postPaths)
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items <- mapM (renderPage "templates/rssitem.xml") pages
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-- Render the result
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renderAndWrite "templates/rss.xml" $ pageFromList [ ("items", concatPages items),
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("url", "rss.xml") ]
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That's that. Now we have a nice rss feed.
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Note that this sorting works because the posts have a
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`yyyy-mm-dd-title.extension` naming scheme. We want the paths as `PagePath` and
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not as `FilePath` or `String`, because `PagePath` is an instance of
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`Renderable`. Also, we only want the 5 most recent posts.
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let renderablePosts = map createPagePath postPaths
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let recentItems = renderAndConcat "templates/postitem.html" $ take 5 renderablePosts
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The `renderAndConcat` function takes a template and a list of `Renderable`
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items. It renders all renderables with the given template, and concatenates the
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result. Note that the concating and reading of pages is not executed yet,
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because of laziness. This helps us, since we want to use the modification
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timestamps of files, and not render everything every time.
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let rssPage = createCustomPage "rss.xml"
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("templates/rssitem.xml" : postPaths) [("items", Right recentItems)]
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We now created the custom rss page. The `createCustomPage` is a function that
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produces a `CustomPage`, which is an instance of `Renderable`. `"rss.xml"` is
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our destination url. We then give a list of extra dependencies that were used
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to generate the custom page, so Hakyll can check modification stamps. The last
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argument is the key-value mapping of our `CustomPage`. Note that the type for
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values is `Either String (IO ByteString)`. So, we can either give a simple
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string, or an IO action that results in a `ByteString`. The benefit of this is
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that the IO action will not be executed if the page in `_site/` is already
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up-to-date. Now, we only need to render it using our rss template.
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renderChain ["templates/rss.xml"] rssPage
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That's it. Now we have a rss feed that is generated only when it is not already
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up-to-date.
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@ -1,5 +1,5 @@
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Name: hakyll
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Version: 0.1
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Version: 0.2
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Synopsis: A simple static site generator library.
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Description:
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