How to Use the Command 'cabal' (with Examples)

Cabal is a command-line interface designed for managing Haskell projects and packages from the Hackage package repository. It serves as an essential tool for Haskell developers, offering functionalities ranging from package management to project creation and building. With Cabal, developers can efficiently handle dependencies, initiate new projects, and automate the build process, significantly enhancing productivity and project maintainability. Below, we delve into various use cases of the Cabal command, illustrating its versatility with practical examples.

Use case 1: Search and List Packages from Hackage

Code:

cabal list search_string

Motivation: When working on a Haskell project, you might need to incorporate additional libraries or tools. Before downloading a package, it’s essential to know its existence and details. cabal list helps you search for packages on Hackage, the central package archive for Haskell libraries. By searching through Hackage, you ensure that you find the most suitable and updated packages for your project’s needs.

Explanation:

• cabal: Invokes the Cabal command-line interface.
• list: This subcommand is used to list available packages. It can display all packages or can filter them based on a search string.
• search_string: A placeholder you replace with actual text to search for specific packages. Using this argument allows you to narrow down the list to relevant packages only.

Example Output:

* HUnit
    Synopsis: A unit testing framework for Haskell
    Default available version: 1.6.0.0
    Installed versions: ---
    Homepage: http://coverage.lcov.io/
    License: BSD3

Use case 2: Show Information About a Package

Code:

cabal info package

Motivation: Understanding a package before integrating it into your project is critical for successful project development. Knowing a package’s version, dependencies, and other key details helps ensure compatibility with your existing system configuration. cabal info enables developers to gain insights into a specific package before proceeding with installation, thus aiding informed decision-making.

Explanation:

• cabal: The command initiates the Cabal functionality.
• info: Requests detailed information about a package.
• package: This is the name of the package for which you want more information. Replace package with the actual package name you are investigating.

Example Output:

* Package: lens
  Synopsis: Lenses, Folds and Traversals
  Version: 4.19.2
  Dependencies: base >=4.7 && <5
  License: BSD3
  Maintainer: Edward Kmett <ekmett@gmail.com>

Use case 3: Download and Install a Package

Code:

cabal install package

Motivation: Installing new packages is a regular task for developers seeking to extend their applications’ functionality. cabal install simplifies this process significantly, enabling developers to download and install packages directly from Hackage. This command makes it easier to include additional libraries that enhance application capabilities without manually handling dependencies.

Explanation:

• cabal: Activates the Cabal command interface.
• install: This subcommand is used to install a package.
• package: The specific package name you want to install. Replacing package with an actual package name downloads and installs that package.

Example Output:

Resolving dependencies...
Configuring text-1.2.4.1...
Building text-1.2.4.1...
Installed text-1.2.4.1

Use case 4: Create a New Haskell Project in the Current Directory

Code:

cabal init

Motivation: Establishing a new Haskell project typically involves setting up the directory structure, creating configuration files, and managing dependencies. cabal init streamlines this process by initializing a project with sensible defaults. This step helps developers kick-start their projects efficiently, saving time and effort on boilerplate tasks.

Explanation:

• cabal: Calls the Cabal application for use.
• init: This subcommand initializes a new Haskell project. It sets up necessary configuration and project files.

Example Output:

Package name? [default: file-name]:
Package version? [default: 0.1.0.0]:
...
Guessing dependencies...
Generating LICENSE...
Generating Setup.hs script file...
Generating README.md...

Use case 5: Build the Project in the Current Directory

Code:

cabal build

Motivation: The building phase of project development involves compiling source files and linking them to create an executable or library. cabal build is crucial during this phase as it automates the process, handling complex build toolchains and dependencies. It ensures that all parts of the project are compiled correctly, thus fostering successful application deployment.

Explanation:

• cabal: Initiates the Cabal command functionalities.
• build: Specifically instructs Cabal to compile and build the project within the current directory.

Example Output:

Building project-1.0.0...
Preprocessing library for project-1.0.0..
Building library for project-1.0.0..
[1 of 1] Compiling Main 
Linking ...

Use case 6: Run Tests of the Project in the Current Directory

Code:

cabal test

Motivation: Testing is a fundamental part of software development, providing assurance that code behaves as expected. With cabal test, developers can execute test suites integrated into their projects effortlessly. This command facilitates continuous integration practices by automating the test execution process, ensuring that new changes do not break existing functionality.

Explanation:

• cabal: Signals the use of Cabal tool.
• test: Directs Cabal to run tests associated with the current project. It searches for test suites defined in the project’s configuration and executes them.

Example Output:

Running 1 test suites...
Test suite my-tests: RUNNING...
Test suite my-tests: PASS

Conclusion:

Cabal provides a comprehensive suite of tools for managing Haskell projects and packages, making Haskell development more efficient and effective. Whether you are searching for libraries, managing dependencies, initializing projects, or automating builds and tests, Cabal’s command-line utilities streamline these processes, supporting both beginner and expert developers in achieving their goals with greater ease.