How to use the command 'yesod' (with examples)
The ‘yesod’ command is a helper tool for Yesod, a Haskell-based web framework. It provides various functionalities for creating, developing, and deploying web applications built with Yesod. All Yesod commands are invoked through the ‘stack’ project manager.
Use case 1: Create a new scaffolded site, with SQLite as backend, in the ‘my-project’ directory
Code:
stack new my-project yesod-sqlite
Motivation: Creating a new scaffolded site is the first step to start building a web application with Yesod. This command sets up a new project with the necessary folder structure and files, using SQLite as the backend database.
Explanation:
- ‘stack new’: This command creates a new project using the stack project manager.
- ‘my-project’: This is the name of the directory where the scaffolded site will be created.
- ‘yesod-sqlite’: This is a template that sets up a new site with SQLite as the backend.
Example output: The command will create a new directory named ‘my-project’ with the scaffolded site structure and files in it.
Use case 2: Install the Yesod CLI tool within a Yesod scaffolded site
Code:
stack build yesod-bin cabal-install --install-ghc
Motivation: Installing the Yesod CLI tool is necessary to perform various development tasks within a Yesod scaffolded site. This command installs the Yesod executable and the cabal-install package.
Explanation:
- ‘stack build’: This command tells stack to build the project’s dependencies.
- ‘yesod-bin’: This is the package name for the Yesod executable.
- ‘cabal-install’: This is the package name for the cabal-install tool.
- ‘–install-ghc’: This flag instructs stack to install GHC (the Glasgow Haskell Compiler) if it’s not already installed.
Example output: The command will install the Yesod CLI tool and the cabal-install package, making them available for use within the Yesod scaffolded site.
Use case 3: Start development server
Code:
stack exec -- yesod devel
Motivation: To develop and test the web application locally, it is necessary to start the development server. This command starts the Yesod development server, allowing you to view and interact with your application in a web browser.
Explanation:
- ‘stack exec’: This command executes a command within the context of the stack project.
- ‘– yesod devel’: This is the command to start the Yesod development server.
Example output: The development server will start running, and you will see the output in the terminal, indicating that the server is listening for requests.
Use case 4: Touch files with altered Template Haskell dependencies
Code:
stack exec -- yesod touch
Motivation: When working with Template Haskell in a Yesod project, changes to the template code might require recompilation of certain files. The ‘yesod touch’ command ensures that the modified files are correctly recompiled when needed.
Explanation:
- ‘stack exec’: This command executes a command within the context of the stack project.
- ‘– yesod touch’: This is the command to touch files with altered Template Haskell dependencies.
Example output: The command will analyze the modified files, determine if recompilation is required, and output the result in the terminal.
Use case 5: Deploy application using Keter (Yesod’s deployment manager)
Code:
stack exec -- yesod keter
Motivation: When the development of a Yesod web application is completed, deploying it to a production environment usually involves using a deployment manager like Keter. The ‘yesod keter’ command helps in creating the Keter bundle for the application.
Explanation:
- ‘stack exec’: This command executes a command within the context of the stack project.
- ‘– yesod keter’: This is the command to deploy the application using Keter.
Example output: The command will generate the Keter bundle, which includes all the necessary files and configurations required to deploy the Yesod application using Keter. The output will indicate the location of the generated bundle.
Conclusion:
The ‘yesod’ command is a powerful tool for managing various aspects of a Yesod web application. It facilitates the creation of new projects, installation of required tools, starting the development server, handling Template Haskell dependencies, and deploying the application using Keter. By understanding and utilizing the different use cases of the ‘yesod’ command, developers can efficiently develop and deploy robust Haskell-based web applications using the Yesod framework.
