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Programming language: Haskell
License: MIT License
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                   developer friendly :: type safe :: performant

1. Rationale  Build Status

LambdaCms is a set of packaged libraries —containing subsites for the Yesod application framework— which allow rapid development of robust and highly performant websites with content management functionality.

The lambdacms-* packages each provide some functionality and can depend on eachother by specifying them as dependencies in their .cabal file. The only mandatory package is lambdacms-core, it provides functionality that all other lambdacms-* packages depend on.

As mentioned, each lambdacms-* package contains a subsite which is "mounted" in a standard Yesod application we call the "base application", or simply "base". To mount a packaged subsite specify it as a dependency to the base app's .cabal file and add some glue code as explained below.

In the base app we have to:

  • configure a database connection,
  • organize the admin backend's menu,
  • specify the authentication strategies for admins, and
  • define admin user roles and their permissions.

In the base app we optionally may also:

  • override default behavior,
  • override UI texts,
  • provide a means to send email notifications, and last but not least,
  • write the themes so the website can actually be visited (recommended).

2. Setting up a site with LambdaCms

This section describes the steps of setting up a site with LambdaCms.

For the purpose of integration testing we also provide a script that covers the steps below. We recommend following the steps below as it provides more guidance and helps to understand the inner workings.

NOTE: We're currently in the process using stack, and upgrading to GHC 7.10. This means we will use Stackage's nightly-2015-07-24 package set until LTS 3 is released.


You need to be reasonably acquinted with Haskell in order to follow along with this guide. To learn basic Haskell skills we recommend Brent Yorgey's excellent Introduction to Haskell course.

Besides Haskell you need to be somewhat familliar with:

  • the web technologies (HTTP, HTML, CSS, JS, REST),
  • RDBMS/SQL (LambdaCms makes use of a relational database), and
  • the Yesod web application framework (for which an awesome book exists).

Non-Haskell dependencies

For the connection with the database, Haskell libraries typically compile against non-Haskell libraries. One of the following libraries needs to be available:

  • For Postgres:

    • Debian/Ubuntu: libpq-dev
    • CentOS/Fedora/RHEL: postgresql-devel
    • Homebrew (OSX): postgres
  • For Mysql:

    • Debian/Ubuntu: libmysqlclient-dev
    • CentOS/Fedora/RHEL: mysql-devel
    • Homebrew (OSX): mysql
  • For Sqlite (required for building the test suite)

    • Debian/Ubuntu: libsqlite3-dev
    • CentOS/Fedora/RHEL: sqlite-devel
    • Homebrew (OSX): sqlite

On other platforms these packages might have different names, but are most likely available.

If you are going to use a database other than Sqlite (which directly writes to a file), you need to have a database accessible from where you run your site. This means you might have to install and setup a database server locally.

Create a project folder

Choose a name for your project. In below we choose mysite, which you probably want to change. Make sure to choose a valid unix file name to avoid naming issues. Now create a directory for your project and cd into it, by running the following commands:


Initializing the base application

First we need to install the yesod command, this command requires a lot of dependent packages to be downloaded and build (may a while).

stack install yesod-bin --resolver nightly-2015-07-24

With the following command you create a "scaffolded" Yesod application. The command is interactive; you need to supply some configuration values. Pick the database of your choice, and choose a project name:

yesod init -n $PROJECT_NAME --bare

If you have chosen a database other than Sqlite, you need to create a database and a sufficiently priviledged database user, and set these credentials in the config/setting.yml file.

Now we will create a stack.yaml file for this project which specifies the nightly snapshot we would like to use.

stack init --resolver nightly-2015-07-24

NOTE: This command complains that the some version constraints in the $PROJECT_NAME.cabal file are too strict. Please raise the upper bounds of these dependencies manually. This step may be removed once LTS 3 is out.

This installs all dependencies and builds the scaffoled application (may take a while):

stack install

When you experience problems during builds, while using LTS 3.x, we consider this a bug. Please raise an issue.

Testing the scaffoled Yesod app

The following commands will run your scaffolded Yesod application in development mode.

stack exec yesod devel

Now fire some requests at it by pointing your browser to: http://localhost:3000

If all went well you are now ready to add LambdaCms to your app.

Patching a freshly init'ed Yesod app scaffold to use lambdacms-core

To add lambdacms-core to a fresh Yesod application scaffold, a number of files need to be edited. We use some patch files to automate this process to a couple of simple shell commands.

Run the following commands from the root of your Yesod application scaffold. It first downloads the patches by cloning the repository in to the /tmp directory. Then the patches are applied with the good old patch command.

export TMP_CLONE=/tmp/lambdacms-clone-for-patches-`date +%s`
git clone --depth=1 https://github.com/lambdacms/lambdacms.git $TMP_CLONE
mv $PROJECT_NAME.cabal project_name.cabal
for f in $TMP_CLONE/yesod-scaffold-patches/*.patch; do patch -p1 < $f; done
mv project_name.cabal $PROJECT_NAME.cabal
rm -rf $TMP_CLONE

If any patches (partly) fail: try to fix it manually editing the files in question. If this happens while closely following this README, then please open an issue.

You could patch the files individually by manually unrolling the for loop in the commands above.

In some cases you may want to do manual patching instead (e.g. for existing web app), in this case you can simply go through .patch files in lambdacms/yesod-scaffold-patches/ subfolder, they are quite self-exlplanatory. Alternatively there is a quick overview.

Configure the initial administrator

By default the application uses Mozilla's Persona to log in: the email address used to log in need to be registered with Persona. It is recommended to use an email address of a Persona account for development as it simplifies logging in during development.

Edit config/settings.yml to insert a valid email address.

admin: "_env:LAMBDACMS_ADMIN:<email address>"

Replace <email address> with the email address of an initial administrator or developer, so the admin inteface can be accessed.


After applying the patches lambdacms-core is installed in your Yesod application. Run stack install again to rebuild and install with the patches.

Then start the development server, which automatically recompiles when files have changed.

stack exec yesod devel

Point your browser to http://localhost:3000/admin and you will be prompted to login. The setup as described above has selected Mozilla's Persona as the only means of authentication. In config/settings.yml you have provided an email address for the admin user that is created if no users exist. If this email address is known to Mozilla Persona then you can procede to log in.

3. Add a LambdaCms "extensions" to your base application

LambdaCms' extension system is one of its core strengths: it allows a developer to extend the site with packages while ensuring full type safety.

Please refer to lambdacms-media's README for installation instructions. It also explains how other LambdaCms extensions may incorporate media items managed by the lambdacms-media extension.

Or of course create your own extension...

4. Creating your own extensions

In order to make the code base of your website as modular as possible, we recommend packaging functionality into LambdaCms extensions. This allows functionality to be shared as a library.

Since this takes a bit of boiler plate, we have released a well documented extension scaffold script that should get you started.

5. Examples

We plan to have more reference material online soon.

Currently the best place to have a look is the code for the lambdacms.org website. It shows how a "base" application is extended with lambdacms-core and lambdacms.org-specific extensions.


All code in this repository is released under the MIT license, as specified in the LICENSE file.

*Note that all licence references and agreements mentioned in the lambdacms-core README section above are relevant to that project's source code only.