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Joseph Cooper
Joseph Cooper

What's New in Cabal Engine V 1002? A Comprehensive Overview


Cabal Engine V 1002: What Is It and How to Use It




If you are a Haskell developer, you probably have heard of Cabal, the common architecture for building applications and libraries in Haskell. Cabal is a system that allows you to manage your project's dependencies, build options, tests, benchmarks, documentation, and more. Cabal is also a tool that helps you create, configure, compile, run, test, and distribute your Haskell projects.




Cabal Engine V 1002



But did you know that there is a new version of Cabal that has been released recently? It is called Cabal Engine V 1002, and it is a major update that brings many new features, improvements, and bug fixes. Cabal Engine V 1002 is the latest version of the Cabal library, which is the core component of the Cabal system. It is also compatible with the latest version of the cabal-install tool, which is the command-line interface for using Cabal.


In this article, we will explore what Cabal Engine V 1002 is, what are its main features and benefits, and how to use it in your Haskell projects. We will also share some tips and tricks for using Cabal Engine V 1002 effectively. By the end of this article, you will have a better understanding of how Cabal Engine V 1002 can help you create high-quality Haskell applications and libraries.


So, let's get started!


Introduction




Cabal Engine V 1002 is the latest version of the Cabal library, which was released on April 1st, 2023. It is a major update that introduces many new features, improvements, and bug fixes. Some of the highlights of Cabal Engine V 1002 are: - Support for GHC 9.2, the latest version of the Glasgow Haskell Compiler, which brings many new language features and optimizations. - Support for cabal.project files, which allow you to specify multiple packages and their dependencies in a single file, making it easier to work with large and complex projects. - Support for remote source repositories, which allow you to depend on packages that are hosted on GitHub, GitLab, or other platforms, without having to download them manually or use submodules. - Support for common stanzas, which allow you to define common settings and options for multiple components in your project, reducing duplication and improving readability. - Support for qualified goals, which allow you to specify different versions or flags for the same package, depending on the context and purpose of the build. - Support for custom setup dependencies, which allow you to specify the dependencies of your custom setup script, ensuring that they are installed and available when building your project. - Support for benchmark sections, which allow you to define and run benchmarks for your project, using various frameworks and tools. - Support for foreign libraries, which allow you to export Haskell functions as C callable interfaces, enabling interoperability with other languages and systems. - Support for Backpack, a new feature of GHC that allows you to write modular and reusable code with abstract interfaces and mixins. - Improved performance, stability, error messages, documentation, and compatibility with other tools and platforms. These are just some of the new features and improvements that Cabal Engine V 1002 offers. You can find more details and examples in the official release notes and the user guide. To use Cabal Engine V 1002, you need to download and install it from the official website or use your preferred package manager. You also need to have cabal-install 3.6 or later, which is the command-line interface for using Cabal. You can check the versions of Cabal and cabal-install by running the following commands in your terminal: cabal --version cabal-install --version


You should see something like this: Cabal library version 3.6.0.0 cabal-install version 3.6.0.0 compiled using version 3.6.0.0 of the Cabal library


If you have older versions of Cabal or cabal-install, you need to update them to use Cabal Engine V 1002. Now that you have Cabal Engine V 1002 installed, let's see how to use it in your Haskell projects. How to Use Cabal Engine V 1002




Cabal Engine V 1002 provides a simple and consistent way to create, configure, compile, run, test, and distribute your Haskell projects. In this section, we will cover some of the most common tasks and commands that you can use with Cabal Engine V 1002.


How to create a cabal project with Cabal Engine V 1002




To create a new cabal project with Cabal Engine V 1002, you can use the cabal init command. This command will ask you some questions about your project, such as its name, version, license, dependencies, etc., and generate a .cabal file and a src directory with some skeleton code for you.


For example, let's create a new cabal project called hello-world. To do this, we can run the following commands in our terminal:


mkdir hello-world cd hello-world cabal init


This will prompt us with some questions about our project, such as:


Please choose a version of the Cabal specification to use: 1) 1.10 (legacy) 2) 2.0 (+ support for Backpack, internal sub-libs, '^>=' operator) 3) 2.2 (+ support for 'common', 'elif', redundant commas, SPDX) 4) 2.4 (+ support for '' globbing) 5) 3.0 (+ support for 'mixins', 'pkgconfig-depends', 'visibility', SPDX license expressions) 6) 3.4 (+ support for 'default-language', 'default-extensions') 7) 3.6 (+ support for 'benchmark' sections) * 8) (default) Use latest supported specification (currently: cabal-version: >=3.6) Your choice? [default: "8"] Package name? [default: hello-world] Package version? [default: 0.1.0.0] Please choose a license: 1) (none) 2) GPL-2.0-only 3) GPL-3.0-only 4) LGPL-2.1-only 5) LGPL-3.0-only 6) AGPL-3.0-only 7) BSD-2-Clause 8) BSD-3-Clause * 9) MIT 10) MPL-2.0 11) Apache-2.0 12) ISC Your choice? [default: "9"] Author name? [default: Your Name] Maintainer email? [default: you@example.com] Project synopsis? A simple hello world program Project category: * 1) (none) 2) Codec 3) Concurrency 4) Control 5) Data 6) Database 7) Development 8) Distribution 9) Game 10) Graphics ... (many more options) Your choice? [default: "1"] What does the package build: 1) Library 2) Executable Your choice? [default: "2"] What is the main module of the executable: * 1) Main.hs (does not yet exist) 2) Main.lhs (does not yet exist) Your choice? [default: "1"] What base language is the package written in: * 1) Haskell2010 2) Haskell98 Your choice? [default: "1"] Add informative comments to each field in the cabal file (y/n)? [default: n] y Guessing dependencies... Generating LICENSE... Generating Setup.hs... Generating hello-world.cabal... Warning: no synopsis given. You should edit the .cabal file and add one. You may want to edit the .cabal file and add a Description field.


This will generate a hello-world.cabal file that looks something like this: -- This file has been generated from package.yaml by hpack version 0.34.4. -- -- see: https://github.com/sol/hpack -- -- hash: e5f9c7a8d6f8c5e4c4f5b7a6b9b7d9f4c8e9a7d6a5e6f7f8c9f9a7b6a5e6f7f8 name: hello-world version: 0.1.0.0 synopsis: A simple hello world program description: Please see the README on GitHub at


homepage: https://github.com/githubuser/hello-world#readme bug-reports: https://github.com/githubuser/hello-world/issues author: Your Name maintainer: you@example.com license: MIT license-file: LICENSE build-type: Simple cabal-version: >=3.6 executable hello-world-exe main-is: Main.hs other-modules: Paths_hello_world hs-source-dirs: src build-depends: base >=4.14 && =3.6 && =0.6 && =1.2 && =0.12 && =1.2 && =0.10 && =2.2 && =0.5 && =4.19 && =1.5 && =2.3 && =1.9 && =3.1 && =0.13 default-language: Haskell2010 default-extensions: OverloadedStrings ghc-options: -Wall -Werror -- Paths module autogen-modules: Paths_hello_world -- Modules included in this executable, other than Main. other-modules: Paths_hello_world -- Extra files to be distributed with the package, such as examples or a README. extra-source-files: README.md -- A short (one-line) description of the package. description: A simple hello world program -- A longer description of the package. -- description: -- URL for the project homepage or repository. homepage: https://github.com/githubuser/hello-world#readme -- The license under which the package is released. license: MIT -- The file containing the license text. license-file: LICENSE -- The package author(s). author: Your Name -- An email address to which users can send suggestions, bug reports, and patches. maintainer: you@example.com -- A copyright notice. -- copyright: category: None build-type: Simple -- Extra files to be distributed with the package, such as examples or a README. extra-source-files: README.md


This file contains all the information and settings for our project, such as its name, version, license, dependencies, build options, etc. We can edit this file manually to customize our project further, or use cabal commands to update it automatically.


In addition to the .cabal file, cabal init also creates a src directory with a Main.hs file that contains some skeleton code for our executable. It looks something like this:


module Main where import qualified Data.Text as T import qualified Data.Vector as V import qualified Data.ByteString as B import qualified Data.Aeson as A import qualified Control.Monad.Trans.Class as C import qualified Control.Monad.Trans.Reader as R import qualified Control.Monad.Trans.State as S import qualified Control.Monad.Trans.Writer as W import qualified Control.Monad.Trans.Maybe as M import qualified Control.Monad.IO.Class as I import qualified Network.HTTP.Simple as H import qualified Text.XML as X import qualified Text.Parsec as P import qualified Data.Attoparsec.Text as A import System.Random (randomRIO) import System.Environment (getArgs) import System.Exit (exitSuccess, exitFailure) import System.IO (hPutStrLn, stderr) import Paths_hello_world (version) import Data.Version (showVersion) main :: IO () main = do args putStrLn $ "hello-world version " ++ showVersion version ["--help"] -> putStrLn usage [] -> putStrLn "Hello, world!" _ -> do hPutStrLn stderr $ "Invalid arguments: " ++ unwords args hPutStrLn stderr usage exitFailure usage :: String usage = "Usage: hello-world [--version] [--help]"


This file contains some imports of common libraries and modules that we might use in our project, such as text, vector, bytestring, aeson, mtl, http-conduit, xml-conduit, parsec, attoparsec, etc. It also defines a simple main function that prints "Hello, world!" or shows the version or usage information depending on the command-line arguments. We can modify this file to implement our own logic and functionality for our executable.


Alternatively, we can also use a cabal.project file to create and manage our cabal project. A cabal.project file is a simple text file that lists the packages and their locations that are part of our project. For example, we can create a cabal.project file that looks something like this:


packages: hello-world/ some-other-package/ https://github.com/someuser/some-repo.git#cabal-v2-branch


This file tells cabal that our project consists of three packages: hello-world, some-other-package, and some-repo. The first two packages are located in subdirectories of our current directory, while the third one is located in a remote GitHub repository. Cabal will automatically download and install the remote package when we build our project.


A cabal.project file allows us to work with multiple packages and their dependencies in a single project. It also allows us to use remote source repositories, which can be useful for depending on packages that are not published on Hackage or other sources. We can also specify various options and settings for our project in a cabal.project file, such as compiler flags, profiling options, etc.


Whether we use a .cabal file or a cabal.project file, we can now build our project with Cabal Engine V 1002. To do this, we can use the cabal build command, which will compile our project and produce an executable file in the dist-newstyle directory. For example, we can run the following command in our terminal: cabal build


This will output something like this: Resolving dependencies... Build profile: -w ghc-9.2.1 -O1 In order, the following will be built (use -v for more details): - hello-world-0.1.0.0 (exe:hello-world-exe) (first run) Configuring executable 'hello-world-exe' for hello-world-0.1.0.0.. Preprocessing executable 'hello-world-exe' for hello-world-0.1.0.0.. Building executable 'hello-world-exe' for hello-world-0.1.0.0.. [1 of 2] Compiling Main ( src/Main.hs, /home/user/hello-world/dist-newstyle/build/x86_64-linux/ghc-9.2.1/hello-world-0.1.0.0/x/hello-world-exe/build/hello-world-exe/hello-world-exe-tmp/Main.o ) [2 of 2] Compiling Paths_hello_world ( /home/user/hello-world/dist-newstyle/build/x86_64-linux/ghc-9.2.1/hello-world-0.1.0.0/x/hello-world-exe/build/hello-world-exe/autogen/Paths_hello_world.hs, /home/user/hello-world/dist-newstyle/build/x86_64-linux/ghc-9.2.1/hello-world-0.1.0.0/x/hello-world-exe/build/hello-world-exe/hello-world-exe-tmp/Paths_hello_world.o ) Linking /home/user/hello-world/dist-newstyle/build/x86_64-linux/ghc-9.2.1/hello-world-0.1.0.0/x/hello-world-exe/build/hello-world-exe/hello-world-exe ...


We can now run our executable file by using the cabal run command, which will execute our program with the given arguments. For example, we can run the following command in our terminal: cabal run hello-world-exe -- --version


This will output something like this: Up to date hello-world version 0.1.0.0


We have successfully created and run our first cabal project with Cabal Engine V 1002! But there is much more that we can do with Cabal Engine V 1002, such as using the interactive REPL, writing and running tests, generating documentation, and more. Let's see how to use some of these features in the next sections. How to use cabal repl with Cabal Engine V 1002




One of the most useful features of Cabal Engine V 1002 is the cabal repl command, which launches an interactive REPL (Read-Eval-Print Loop) for our project.


A REPL is a tool that allows us to interactively evaluate expressions and commands in our programming language, without having to compile and run a whole program.


With cabal repl, we can load our project's modules and dependencies into a GHCi session, where we can experiment with our code, test functions, inspect types and values, and more.


To use cabal repl, we can simply run the following command in our terminal:


cabal repl


This will output something like this:


Resolving dependencies... Build profile: -w ghc-9.2.1 -O1 In order, the following will be built (use -v for more details): - hello-world-0.1.0.0 (exe:hello-world-exe) (first run) Configuring executable 'hello-world-exe' for hello-world-0.1.0.0.. Preprocessing executable 'hello-world-exe' for hello-world-0.1.0.0.. GHCi, version 9.2.1: https://www.haskell.org/ghc/ :? for help [1 of 2] Compiling Main ( src/Main.hs, interpreted ) [2 of 2] Compiling Paths_hello_world ( /home/user/hello-world/dist-newstyle/build/x86_64-linux/ghc-9.2.1/hello-world-0.1.0 .0/x/hello-world-exe/build/hello-world-exe/autogen/Paths_hello_world.hs, interpreted ) Ok, two modules loaded. Loaded GHCi configuration from /home/user/.ghci *Main Paths_hello_world>


We are now in the GHCi prompt, where we can type expressions and commands and see their results. For example, we can type the following expression and press enter:


*Main Paths_hello_world> 2 + 2


This will output something like this:


4


We can also load our project's modules and use their functions and values. For example, we can type the following command and press enter:


*Main Paths_hello_world> :l Main


This will output something like this:


[1 of 2] Compiling Main ( src/Main.hs, interpreted ) [2 of 2] Compiling Paths_hello_world ( /home/user/hello-world/dist-newstyle/build/x86_64-linux/ghc-9.2.1/hello-world-0.1.0.0/x/hello-world-exe/build/hello-world-exe/autogen/Paths_hello_world.hs, interpreted ) Ok, two modules loaded. *Main>


We have now loaded the Main module, which contains our main function and other definitions. We can use them in the GHCi prompt. For example, we can type the following expression and press enter:


*Main> main


This will output something like this:


Hello, world!


We can also use the :t command to inspect the types of expressions and values. For example, we can type the following command and press enter:


*Main> :t main


This will output something like this:


main :: IO ()


This tells us that main is a value of type IO (), which means it is an action that performs some input/output operations and returns nothing.


We can also use the :i command to get more information about types, classes, modules, etc. For example, we can type the following command and press enter:


*Main> :i T.Text


This will output something like this:


data T.Text = T.Text -# UNPACK #-!(A.Array T.Word16) -# UNPACK #-!Int -# UNPACK #-!Int -- Defined in Data.Text.Internal instance Eq T.Text -- Defined in Data.Text.Internal instance Ord T.Text -- Defined in Data.Text.Internal instance Show T.Text -- Defined in Data.Text.Internal instance Read T.Text -- Defined in Data.Text.Internal instance Monoid T.Text -- Defined in Data.Text.Internal instance Semigroup T.Text -- Defined in Data.Text.Internal instance NFData T.Text -- Defined in Data.Text.Internal instance A.IsString T.Text -- Defined in Data.Text.Internal instance Binary T.Text -- Defined in Data.Binary.Instances instance Hashable T.Text -- Defined in Data.Hashable.Class instance Generic T.Text -- Defined in


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