• To install Haskell packages to your project using Cabal, you can follow these steps:

1. Add dependencies to your .cabal file: You need to specify the packages your project depends on under the build-depends field in your .cabal file. This is where you declare the Haskell packages your project relies on. For example, if you want to add a package called text, you would modify the build-depends field like so:

       build-depends:    
       base ^>=4.17.2.1,
       text ^>=1.2.4.0

2. Update dependencies: After modifying the .cabal file, you need to update your project's dependencies. Open a terminal, navigate to your project directory, and run:

   cabal update

   This command updates the package index, ensuring you have the latest information about available packages.

3. Install dependencies: Once you've updated the package index, you can install the dependencies specified in your .cabal file by running:

   cabal install --only-dependencies

   This command installs the dependencies listed in your .cabal file, but it does not install the project itself. It's useful for fetching and installing the required packages.

4. Build your project: After installing the dependencies, you can build your project by running:

   cabal build

   This command compiles your project and generates the necessary executables.

5. Run your project: If your project produces an executable, you can run it using:

   cabal run <executable-name>

   Replace <executable-name> with the name of your executable as specified in your .cabal file.

Following these steps should allow you to install Haskell packages to your project using Cabal. Make sure to replace text with the actual package names you want to install.

In case there are any missing dependencies

You may encounter an error while trying to install the zlib package, which is a dependency of scotty. The error message indicates that cabal is unable to find the necessary header file (zlib.h) and C library (z) for zlib.

Here are a few steps you can take to resolve this issue:

1. Install the zlib Development Package: You'll need to install the development package for zlib, which usually includes the necessary header files and libraries required for development. On most Linux distributions, this package is typically named something like zlib-devel or zlib1g-dev. You can install it using your package manager. For example, on Ubuntu, you can run:

   sudo apt-get install zlib1g-dev

   On CentOS/RHEL:

   sudo yum install zlib-devel

   On macOS with Homebrew:

   brew install zlib

2. Specify Include and Library Directories: If you have installed zlib in a non-standard location, you may need to specify the include and library directories using the --extra-include-dirs and --extra-lib-dirs flags when running cabal install. For example:

   cabal install scotty --extra-include-dirs=/path/to/zlib/include --extra-lib-dirs=/path/to/zlib/lib

3. Verify zlib Installation: After installing the zlib development package, make sure that the zlib.h header file and the z library are accessible in the standard locations.

4. Check Build Logs: If the issue persists, you can try re-running cabal with increased verbosity (-v3) to get more detailed error messages. This might help pinpoint the exact problem.

Once you've resolved the issue with zlib, you should be able to successfully install scotty using cabal.

Verifying dependency installation

You can use the dpkg command to query information about installed packages on Debian-based systems like Debian itself or Ubuntu. Here's how you can check for the path of zlib using dpkg:

dpkg -L zlib1g-dev

This command lists all the files installed by the zlib1g-dev package, including the location of header files like zlib.h.

If you want to check for the path of the zlib library itself (libz), you can use:

dpkg -L zlib1g

This will show you the location of the library file (libz.so) and any other files installed by the zlib1g package.

If zlib1g-dev is not installed, you might want to install it using apt:

sudo apt update
sudo apt install zlib1g-dev

Once you have zlib1g-dev installed, you can use dpkg -L to find its path as described above.