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Haskell’s Cabal package is an essential tool in Haskell development. It can be used in setting up new Haskell projects, managing dependencies and building packages. It can also fetch packages from Github, making your development process smoother. Cabal is a system for building and packaging Haskell libraries and programs. It defines a common interface for authors of applications and libraries to express their code’s dependencies on other packages. The remarkable aspect of Cabal is how it integrates with Hackage, a public collection of open-source software written in Haskell.
The predicament arises when we’re dealing with Haskell projects that are not available in Hackage repository and hosted on other platforms like GitHub. For such cases, Cabal by default does not support fetching packages directly from GitHub.
The best way to resolve this issue is to directly download the GitHub package and install it locally using Cabal. It requires manual work but ensures the desired GitHub package’s seamless integration into your Haskell project.
Here is a step-by-step guide:
- First, navigate to the GitHub repository of the package you want to install.
- Then, download the package. This can be done by clicking on the ‘Code’ button and then selecting ‘Download ZIP’.
- After downloading, extract the contents of the ZIP file to a convenient location on your machine.
- Navigate to the directory containing the package using the terminal command line.
- Once you’re in the correct directory, use the following command to install the package using Cabal:
This command will install the package in your local machine.
Understanding the Cabal Code
The command ‘cabal install’ tells Cabal to build and install the package available in the present directory. Cabal also fetches any dependencies if they’re not already installed. Once the process is finished, the package is ready to import in your Haskell program.
Relevant Haskell Libraries
Cabal is even more efficient when paired with the appropriate Haskell libraries. A notable library is the ‘HTTP’, largely employed in fetching data from web servers.
Another important library is ‘process’, which comes in handy when you’re executing shell commands from your Haskell code, enhancing the automation capabilities of your code.
Advanced Usage of Cabal
Cabal also allows advanced settings for more complicated scenarios, for instance, when your package relies on the specific version of another package. In this case, the cabal.config file is used. You cannot generate this file automatically. Instead, it’s created manually to define package constraints.
Understanding Cabal’s workings can make work with Haskell significantly more efficient. By properly utilizing Cabal’s systems, you can install diverse packages from GitHub or other platforms without much hassle, whether for web development, database management, or machine learning.