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Juan Pedro Villa

Dr. Hakyll: Create a GitHub page with Hakyll and CircleCI


Hakyll is a Haskell library and program for creating static sites such as simple blogs. Hakyll sites are configured in Haskell in a similar way to xmonad. Moreover, Hakyll sites use Pandoc, which means content can be written in markup languages like Markdown and LaTeX.

Getting started with Hakyll is easy thanks to the Hakyll tutorials and examples. In addition, there are several blog posts about how to build and publish a Hakyll site:

After using services such as Blogger and WordPress.com, and taking a look at tools like Jekyll (which inspired Hakyll), I finally decided to create a blog with Hakyll, GitHub Pages, and CircleCI. Here are the steps I followed.

Configure Git and GitHub

GitHub Pages gives you one user (and organization) site and one project site for each of your repositories. The most important difference between user and project sites is that GitHub uses the master branch to publish user sites and the gh-pages branch to publish project sites.

To create a user or organization site:

  • Create a GitHub repository named username.github.io, where username is your GitHub username or organization name.

  • Create an empty Git repository for your site, commit, and push:

    $ mkdir username.github.io/
    $ cd username.github.io/
    $ git init
    $ git commit --allow-empty -m "Create master branch"
    $ git remote add origin git@github.com:username/username.github.io.git
    $ git push -u origin master

    The master branch is used by GitHub to publish your site. This is just an empty commit to create the branch. When your site is ready, you can push to master manually, but the idea is to have a continuous integration service do that for you.

  • Create an orphan branch named hakyll for the source of your site:

    $ git checkout --orphan hakyll

    The hakyll branch will contain your site's configuration and content.

  • Add your GitHub repository as a Git submodule at _site, commit, and push:

    $ git submodule add git@github.com:username/username.github.io.git _site
    $ git commit -m "Create hakyll branch"
    $ git push -u origin hakyll

    GitHub Pages is not designed to work immediately with tools like Hakyll. Since Hakyll generates your site in a directory called _site, you can use that directory to update the site published by GitHub.

To create a project site for an existing GitHub repository, use gh-pages instead of master:

  • Create an orphan branch named gh-pages, commit, and push:

    $ git clone git@github.com:username/repository.git
    $ cd repository/
    $ git checkout --orphan gh-pages
    $ git rm -rf .
    $ git commit --allow-empty -m "Create gh-pages branch"
    $ git push origin gh-pages
  • Create an orphan branch named hakyll for the source of your site, add the GitHub repository as a submodule at _site, commit, and push:

    $ git checkout --orphan hakyll
    $ git rm -rf .
    $ git submodule add git@github.com:username/repository.git _site
    $ git commit -m "Add hakyll branch"
    $ git push -u origin hakyll

The following instructions assume that you're creating a user (or organization) site. If you're creating a project site, the instructions are very similar, but use the gh-pages branch instead of master.

Configure Hakyll

The easiest way to configure Hakyll is to use the hakyll-init program as described in the installation instructions. Basically:

  • Install Hakyll:

    $ cabal install hakyll
  • Create the example site:

    $ hakyll-init .
  • Configure and build:

    $ cabal configure
    $ cabal build
  • Generate the site:

    $ cabal run build

    Run the preview server:

    $ cabal run watch

    And go to http://localhost:8000/.

  • If you change the configuration of your site, rebuild it:

    $ cabal run clean
    $ cabal run build

    Or:

    $ cabal run rebuild

As another option, use the Dr. Hakyll sample project. It's a Hakyll site that can be used as a complement to Hakyll's sample site:

(See Bryn Keller's blog for an example of a static site created with Hakyll and the Bootstrap blog example.)

Once your site is ready, add and commit all changes (except _cache, _site, and other Haskell ignored files):

$ git add --all
$ git commit -m "Configure Hakyll"

You can now push the changes or wait until CircleCI is configured:

$ git push origin hakyll

Configure CircleCI

To configure CircleCI, follow your GitHub repository, add a user key to the SSH keys in your project's settings, and make sure it's selected by default.

Now, create a circle.yml file and add your configuration:

  • Add a GHC version to the machine configuration:

    machine:
    
      ghc:
        version: 7.8.4

    Or:

    machine:
    
      ghc:
        version: 7.10.1
  • Override the dependencies section to install dependencies and configure the package:

    dependencies:
    
      override:
        - cabal update
        - cabal sandbox init
        - cabal install --only-dependencies -j
        - cabal configure
  • Override the test section to simply build the package:

    test:
    
      override:
        - cabal build

    If building succeeds, CircleCI should initialize and update the _site submodule, and switch to the master (or gh-pages) branch there. Adittionally, it should generate your site:

      post:
        - git submodule init
        - git submodule update
        - cd _site/ && git checkout master
        - cabal run build
  • Add a deployment section to update your site every time you push to the hakyll branch. First, push all changes in _site to master using the current date and time as reference in the commit message. Also, add [ci skip] to make CircleCI skip building master:

    deployment:
    
      production:
        branch: hakyll
        commands:
          - git config --global user.email circleci@circleci
          - git config --global user.name CircleCI
          - cd _site/ && git status
          - cd _site/ && git add --all
          - cd _site/ && git commit -m "Update (`date '+%F %T %Z'`) [ci skip]"
          - cd _site/ && git push origin master

    Second, update the submodule in the hakyll branch. A Git submodule is a static reference to a specific commit in a repository. In this case, the hakyll branch has a reference to a commit in the master branch. Since the master branch was just updated, the reference in hakyll must be updated to point to the latest commit. CircleCI should just add _site and push. Again, add [ci skip] to the commit message to avoid building everything again. For more information about Git submodules, see the reference or Nicola Paolucci's Git submodules.

          - git status
          - git add _site/
          - git commit -m "Update _site (`date '+%F %T %Z'`) [ci skip]"
          - git push origin hakyll
  • If you want to use your time zone with the date command, add it to the machine configuration:

    machine:
    
      ...
    
      timezone:
        America/Guayaquil

    Or directly to the date command:

    TZ=America/Guayaquil date '+%F %T %Z'

Finally, push your changes:

$ git add circle.yml
$ git commit -m "Configure CircleCI"
$ git push origin hakyll

Once CircleCI is done building your site, you're done. Go to http://username.github.io.

Notes

I think Hakyll is an excellent static site generator. The examples and tutorials make it even better. And it's Haskell. However, there are some things that don't work immediately which are worth mentioning:

Comments

By default, there are no comments in a Hakyll blog. There are several examples of sites proudly generated by Hakyll that use services such as Disqus, which is good enough for me.

Drafts

By default, Hakyll has no way to work with drafts. But you can configure your site to do so. For detailed information about one way to do it, see Drafts in Hakyll by Jorge Israel Peña.

Since Hakyll sites can be used with Git and GitHub, my favorite solution for drafts is simply creating a separate branch and using a pull request for each post. You can preview your site, but it'll only include the draft if you merge it to the hakyll branch.

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