--- title: The basics author: Jasper Van der Jeugt --- ## Let's get started! We're going to discuss a small brochure site to start with. You can find all code and files necessary to build this site [right here](http://github.com/jaspervdj/hakyll-examples/tree/master/brochure) -- feel free to look at them as we go trough the tutorial. To fetch all examples in order to play with them locally, use: git clone git://github.com/jaspervdj/hakyll-examples.git or navigate to the download menu on GitHub. Now, for this first tutorial, there's a number of files we will use: about.rst A simple page written in RST format code.lhs Another page with some code (which can be highlighted) css Directory for CSS files |- default.css The main CSS file \- syntax.css CSS file for code syntax highlighting hakyll.hs Our code to generate the site images Directory for images \- haskell-logo.png The logo of my favorite programming language index.markdown A simple page in markdown format templates Directory for templates \- default.html The main template for the site By default, hakyll will compile everything to the `_site` directory. We can try this like this: [jasper@phoenix] ghc --make hakyll.hs [jasper@phoenix] ./hakyll build Instead of using `build`, we can also use `preview`, which will fire up a webserver serving the `_site` directory, so have a look! All files have been compiled, and their output has been placed in the `_site` directory as illustrated in this diagram: ![Brochure files](/images/brochure-files.png) No magic is involved at all -- we will precisely study how and why our items are compiled like that. All of this is specified in the `hakyll.hs` file. You can view the full `hakyll.hs` file online [here][brochure-hakyll.hs], or you can look in the directory you cloned or downloaded. [brochure-hakyll.hs]: http://github.com/jaspervdj/hakyll-examples/blob/master/brochure/hakyll.hs ## Images Let's start of with the `images/haskell-logo.png` file, because the processing of this file is very simple: it is simply copied to the output directory. Let's look at the relevant lines in the `hakyll.hs` file: ~~~~~{.haskell} match "images/*" $ do route idRoute compile copyFileCompiler ~~~~~ The first line specifies we will describe the process for compiling everything in the `images/` folder: hakyll uses globs for this [^pattern]. [^pattern]: A little caveat is that these globs are not `String`s but `Pattern`s, so you need the `OverloadedStrings` extension. We can see two simple rules next: [route] and [compile]. - [route] determines how the input file(s) get mapped to the output files. [route] only deals with file names -- not with the actual content! - [compile], on the other hand, determines how the file content is processed. [route]: /reference/Hakyll-Core-Rules.html#v:route [compile]: /reference/Hakyll-Core-Rules.html#v:compile In this case, we select the [idRoute]: which means the file name will be kept the same (`_site` will always be prepended automatically). This explains the name of [idRoute]: much like the `id` function in Haskell, it also maps values to themselves. [idRoute]: /reference/Hakyll-Core-Routes.html#v:idRoute For our compiler, we use [copyFileCompiler], meaning that we don't process the content at all, we just copy the file. [copyFileCompiler]: /reference/Hakyll-Core-Writable-CopyFile.html#v:copyFileCompiler ## CSS If we look at how the two CSS files are processed, we see something which looks very familiar: ~~~~~{.haskell} match "css/*" $ do route idRoute compile compressCssCompiler ~~~~~ Indeed, the only difference with the images is that have now chosen for [compressCssCompiler] -- a compiler which *does* process the content. Let's have a quick look at the type of [compressCssCompiler]: [compressCssCompiler]: /reference/Hakyll-Web-CompressCss.html#v:compressCssCompiler ~~~~~{.haskell} compressCssCompiler :: Compiler Resource String ~~~~~ Intuitively, we can see this as a process which takes a `Resource` and produces a `String`. - A `Resource` is simply the Hakyll representation of an item -- usually just a file on the disk. - The produced string is the processed CSS. We can wonder what Hakyll does with the resulting `String`. Well, it simply writes this to the file specified in the `route`! As you can see, routes and compilers work together to produce your site. ## Templates Next, we can see that the templates are compiled: ~~~~~{.haskell} match "templates/*" $ compile templateCompiler ~~~~~ Let's start with the basics: what is a template? An example template gives us a good impression: ~~~~~ Hakyll Example - $$title$$

$$title$$

$$body$$ ~~~~~ A template is a text file to lay out some content. The content it lays out is called a page -- we'll see that in the next section. The syntax for templates is intentionally very simplistic. You can bind some content by referencing the name of the content *field* by using `$$field$$`, and that's it. You might have noticed how we specify a compiler (`compile`), but we don't set any `route`. Why is this? We need to compile the template because we will need it later. If we compile a page later using `templates/default.html`, Hakyll needs to know what `templates/default.html` is. Note that we could move template compilation to the bottom of our code. The order doesn't matter -- Hakyll will determine that for you. But if you don't compile `templates/default.html` as a template, Hakyll will not be able to take it into account when deciding the compilation order. So, the `compile` needs to be there -- but why don't we set a `route` here? Precisely because we don't want to our template to end up anywhere in our site directory! We want to use it to lay out other items -- so we need to load (compile) it, but we don't want to give it a real destination. By using the `templates/*` pattern, we compile all templates in one go. ## Pages The code for pages looks suspiciously more complicated: ~~~~~~{.haskell} match (list ["about.rst", "index.markdown", "code.lhs"]) $ do route $ setExtension "html" compile $ pageCompiler >>> applyTemplateCompiler "templates/default.html" >>> relativizeUrlsCompiler ~~~~~~ But we'll see shortly that this actually fairly straightforward. Let's begin by exploring what a *page* is. ~~~~~~ --- title: Home author: Jasper --- So, I decided to create a site using Hakyll and... ~~~~~~ A page consists of two parts: a body, and metadata. As you can see above, the syntax is not hard. The metadata part is completely optional, this is the same page without metadata: ~~~~~~ So, I decided to create a site using Hakyll and... ~~~~~~ Hakyll supports a number of formats for the page body. Markdown, HTML and RST are probably the most common. Hakyll will automatically guess the right format if you use the right extension for your page. ~~~~~~{.haskell} match (list ["about.rst", "index.markdown", "code.lhs"]) $ do ~~~~~~ We see a more complicated pattern here. Some sets of files cannot be described easily by just one pattern, and here the [list] function can help us out. In this case, we have three specific pages we want to compile. [list]: /reference/Hakyll-Core-Identifier-Pattern.html#v:list ~~~~~~{.haskell} route $ setExtension "html" ~~~~~~ For our pages, we do not want to use `idRoute` -- after all, we want to generate `.html` files, not `.markdown` files or something similar! The [setExtension] route allows you to simply replace the extension of an item, which is what we want here. [setExtension]: /reference/Hakyll-Core-Routes.html#v:setExtension ~~~~~~{.haskell} compile $ pageCompiler >>> applyTemplateCompiler "templates/default.html" >>> relativizeUrlsCompiler ~~~~~~ How should we process these pages? [pageCompiler] is the default compiler for pages. [pageCompiler] does a few things: - It parses the page into body and metadata - It adds some extra metadata fields such as `$$url$$` and `$$path$$` (you shouldn't worry about these for now) - It fill in possible `$$key$$`'s in it's own body - It renders the page using pandoc Which basically means that we end up with a `Page` that has the HTML content we want as body. But we don't just want the plain content on our website -- we want to decorate it with a template, for starters. [pageCompiler]: /reference/Hakyll-Web-Page.html#v:pageCompiler Different compilers can be chained in a pipeline-like way using Arrows. Arrows form a complicated subject, but fortunately, most Hakyll users need not be concerned with the details. If you are interested, you can find some information on the [Understanding arrows] page -- but the only thing you really *need* to know is that you can chain compilers using the `>>>` operator. [Understanding arrows]: http://en.wikibooks.org/wiki/Haskell/Understanding_arrows The `>>>` operator is a lot like a flipped function composition (`flip (.)`) in Haskell, with the important difference that `>>>` is more general and works on all Arrows -- including Hakyll compilers. Here, we apply three compilers sequentially: 1. We load and render the page using `pageCompiler` 2. We apply the template we previously loaded using [applyTemplateCompiler] 3. We relativize the URL's on the page using [relativizeUrlsCompiler] [applyTemplateCompiler]: /reference/Hakyll-Web-Template.html#v:applyTemplateCompiler [relativizeUrlsCompiler]: /reference/Hakyll-Web-RelativizeUrls.html#v:relativizeUrlsCompiler Relativizing URL's is a very handy feature. It means that we can just use absolute URL's everywhere in our templates and code, e.g.: ~~~~~{.haskell} ~~~~~ Using the [relativizeUrlsCompiler], Hakyll will change this to: ~~~~~{.haskell} ~~~~~ when we are compiling `index.html`, or ~~~~~{.haskell} ~~~~~ when we are compiling (some imaginary) `posts/foo.html`. So Hakyll will translate this to a relative URL for each page. This means we can host our site at `example.com` and `example.com/subdir` without changing a single line of code. More tutorials are in the works...