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[[Category:Programming languages]]
[[ja:Haskell]]
{{Related articles start}}
{{Related|Haskell package guidelines}}
{{Related articles end}}

From [[Wikipedia:Haskell (programming language)|Wikipedia]]:
:[https://www.haskell.org Haskell] is a general-purpose, statically typed, purely functional programming language with type inference and lazy evaluation. Developed to be suitable for teaching, research and industrial application, Haskell has pioneered a number of advanced programming language features such as type classes, which enable type-safe operator overloading. Haskell's main implementation is the Glasgow Haskell Compiler (GHC). It is named after logician Haskell Curry.

== Installation ==

There are several choices for Haskell installation. One is supported by Arch Linux, while others are officially supported by Haskell for any Linux distribution.

Since version [https://gitlab.archlinux.org/archlinux/packaging/packages/ghc/-/commit/ced89ede2cb41cd51e9138a643509bbb6d8854cd 8.0.2-1], the Arch {{Pkg|ghc}} package and all [https://archlinux.org/packages/?q=haskell haskell-*] packages in ''extra'' provide only dynamically linked libraries.

Using dynamic linking typically results in faster builds and smaller disk and RAM usage (by sharing pages between multiple running Haskell programs), and will free you from troubleshooting cross-GHC mixing errors. For this reason using [[pacman]] and the [[official repositories]] is preferred for managing end-user applications. But it has its own disadvantage: '''all tools you install from source will break''' on every update of {{Pkg|ghc}}, {{Pkg|ghc-libs}} or [https://archlinux.org/packages/?q=haskell haskell-*] packages since libraries compiled with GHC do not provide a stable [[Wikipedia:Application binary interface|ABI]]. When running such broken binary, you will see the usual message:

{{ic|error while loading shared libraries: libHS...so: cannot open shared object file: No such file or directory}}

To fix this, just rebuild and reinstall the broken tool in order to relink it to newer libraries.

{{Note|For a detailed explanation of why Arch moved to dynamic linking for Haskell packages, see this [https://www.reddit.com/r/linux/comments/9emwtu/arch_linux_ama/e5qssdz maintainer's response].}}

On the other hand, static linking is generally easier to maintain, does not force you to rebuild all tools from source after every update of their dependencies and is currently better supported by the GHC. For these reasons, static linking is the preferred and recommended option for local development. Otherwise, if you want dynamic linking, to link successfully one must configure GHC, Cabal and Stack for this, as the default is to use static linking.

* To install Haskell from Arch [[official repositories]] using [[pacman]], continue reading [[#Native installation]]. Note that this might install several hundred {{ic|haskell-*}} packages into your system.
* Otherwise, skip to the section [[#Alternate installations]].

If you wish to use {{Pkg|ghc}} (from the [[official repositories]]) with static linking, it is possible, but is more complex to setup, see [[#Static linking]].

== Native installation ==

To use Haskell, [[install]] the following packages:

# {{Pkg|ghc}} — A Haskell compiler. There are several [https://www.haskell.org/haskellwiki/Implementations implementations] available, but the one used most (which is now ''de facto'' the reference) is the [https://www.haskell.org/ghc GHC] (Glasgow Haskell Compiler).
# {{Pkg|cabal-install}} or {{Pkg|stack}} — Build tools that rely on GHC to compile Haskell sources. [https://www.haskell.org/cabal Cabal] is the classic build tool focused on dependency resolution and source packages from [https://hackage.haskell.org Hackage] (Haskell community's central package archive of open source software). [https://www.haskellstack.org Stack] is another build tool focused on curated snapshots and source packages from [https://www.stackage.org Stackage] (a stable subset of Hackage that provides curated sets (snapshots) of packages known to work well with each other).

{{Tip|Both Cabal and Stack are stable and mature build tools. Many Haskell developers use Cabal, while many others prefer Stack. If you are not sure which tool to choose, try to install both and see which one works best for you.}}

=== Configuration ===

{{Note|You can skip this section if you are not going to compile Haskell from source, and just use Haskell applications distributed in the repositories.}}

==== Invoking GHC directly ====

In order to link successfully one must pass the {{ic|-dynamic}} flag to GHC. You can try it with the following file:

{{hc|Main.hs|2=
main = putStrLn "Hello, World"
}}

Compile and run it with:

{{hc|
$ ghc -dynamic Main.hs
$ ./Main|
Hello, World
}}

==== Configuring Cabal for dynamic linking ====

First, run the following command to download the latest list of packages from Hackage and create global configuration file {{ic|~/.cabal/config}} (or the file {{ic|$CABAL_CONFIG}} points to):

 $ cabal update

{{Tip|It is advisable to periodically run {{ic|cabal update}} to synchronize your local list of packages and dependencies with the newest version on Hackage.}}

To configure Cabal for dynamic linking, uncomment and edit the following options in {{ic|~/.cabal/config}}:

{{hc|~/.cabal/config|
library-vanilla: False
shared: True
executable-dynamic: True
program-default-options
  ghc-options: -dynamic
}}

* {{ic|library-vanilla: False}} suppresses the creation of static libraries (if your project contains a library).
* {{ic|shared: True}} enables the creation of shared libraries (if your project contains a library).
* {{ic|executable-dynamic: True}} causes dynamic linking to be used for executables (if your project contains executables).
* {{ic|ghc-options: -dynamic}} adds the {{ic|-dynamic}} flag to every invocation of GHC (e.g. if a package has a non-trivial {{ic|Setup.hs}}).

==== Configuring Stack for dynamic linking ====

You can use {{ic|stack setup}} command to initialize Stack and create global configuration file {{ic|~/.stack/config.yaml}}. By default Stack will automatically download its own version of GHC to an isolated location upon first invocation. To force Stack to use system GHC installation instead, run {{ic|stack setup}} with {{ic|--system-ghc}} and {{ic|--resolver}} flags:

 $ stack setup --system-ghc --resolver ''resolver''

Note that you need to specify a resolver which is compatible with your system GHC. Otherwise Stack will happily ignore {{ic|--system-ghc}} flag and download its own copy of GHC. You can determine the version of system GHC using {{ic|ghc --version}} command:

{{hc|$ ghc --version|
The Glorious Glasgow Haskell Compilation System, version 8.10.2
}}

Then visit [https://www.stackage.org Stackage] website and pick a suitable Long Term Support (LTS) or nightly snapshot matching your system GHC version. Use the selected snapshot for {{ic|--resolver}} flag on the command line, e.g. {{ic|--resolver lts-16.15}} or {{ic|--resolver nightly-2020-09-01}}.

Stackage typically lags behind new GHC releases. It may happen that no Stackage snapshot for your system GHC has yet been released. In this case you might want to choose a snapshot for some earlier minor version of GHC or temporarily downgrade your Haskell installation and wait until support for newer GHC releases finally lands on Stackage.

To configure Stack for dynamic linking, add the following snippet to {{ic|~/.stack/config.yaml}}:

{{hc|~/.stack/config.yaml|
# Stop downloading GHCs into isolated locations under ~/.stack.
install-ghc: false

# Allow Stack to pick the system GHC (false by default).
system-ghc: true

# Allow to use, say, Stackage snapshot for GHC 8.8.2 with system GHC 8.8.3.
compiler-check: newer-minor

# Add the -dynamic flag to every invocation of GHC.
ghc-options:
  "$everything": -dynamic
}}

== Package management ==

Most of Haskell libraries and executables are distributed in units of source packages available from Hackage and Stackage. Repositories used by Cabal and Stack respectively.

GHC, the standard compiler for Haskell, generates machine code that can be run natively on Linux. As is common in other compiled languages, a number of popular Haskell packages are available from official Arch repositories in pre-built form.

Some additional packages can be installed from [[AUR]]. This packages may need to build from source, building [[AUR]] packages or developing software require a compiler and build tools to be installed. Using the [[#Native installation]] method is discouraged for this use case, instead see [[#Alternate installations]].

Therefore there are four main sources for Haskell packages: Hackage (Cabal), Stackage (Stack), [[official repositories]] and [[AUR]].

The following table summarizes the advantages and disadvantages of different package management styles.

{| class="wikitable"
! '''Method'''
! '''Pros'''
! '''Cons'''
|-
| Official repositories ||
* Easier package management using [[pacman]]
* Already compiled dynamically linked
||
* Not all packages available
* Makes difficult compiling from source
|-
| Cabal ||
* All packages available
* Root not required
* Better support for development
||
* Installed in home directory
* Difficult to remove specific packages
|-
| Stack ||
* All packages available (favors Stackage)
* Root not required
* Better support for development
||
* Installed in home directory
* Versions are pinned to snapshot
* Difficult to remove specific packages
|-
| AUR ||
* Additional packages available
||
* Risk of unmaintained or orphaned packages
* Incompatible versions of packages possible
|-
|}

=== Cabal ===

{{Note|In Haskell, the term ''Cabal'' can refer to either:
* Cabal file format that describes Haskell packages and their dependencies;
* Cabal library that works with Cabal file format;
* {{ic|cabal}} command-line tool (provided by {{Pkg|cabal-install}} or {{AUR|cabal-install-bin}} packages) that uses Cabal library to build Haskell packages.
In the context of this article, ''Cabal'' usually means {{ic|cabal}} command-line tool unless specified otherwise.}}

Cabal is "the original" build system for Haskell. Most of libraries and tools you can find on Hackage can be installed via Cabal.

==== Installing packages ====

To run user-wide executables installed by Cabal, {{ic|~/.cabal/bin}} must be added to the {{ic|$PATH}} [[environment variable]].

 PATH="$HOME/.cabal/bin:$PATH"

Run the following command to install a Hackage package and all of its dependencies in a single step:

 $ cabal install ''package''

{{Warning|If you are using ''cabal'' from the [[official repositories]], as of December 2024 Cabal [https://github.com/haskell/cabal/issues/6505 ignores] {{ic|ghc-options}} from {{ic|~/.cabal/config}} while building packages with {{ic|build-type: Custom}}. Therefore, it is necessary to specify {{ic|1=--ghc-options=-dynamic}} flag on the command line  otherwise you might experience build errors.}}

You can also build and install a Haskell package from source. To do this, run {{ic|cabal install}} without specifying any package in the directory with the sources.

Each Cabal package should specify a list of its dependencies and their version constraints in the {{ic|.cabal}} file according to the [https://pvp.haskell.org Package Versioning Policy] (PVP). During the package installation, Cabal tries to find a set of dependencies that satisfies all the constraints. This process is called ''dependency resolution''.

There are reasons why Stack exists; Cabal is known to generate a lot of friction with beginners, although it has been getting better in the past years. Most of the time dependency resolution works well but sometimes it fails. In this case you will need to figure out the cause of the problem and give Cabal some hints about how to resolve offending dependencies. For example, sometimes it is necessary to add {{ic|--allow-newer}} to allow Cabal to ignore package's PVP-dictated upper bounds on dependency versions, effectively installing package with newer dependencies than the package author has permitted. It gets hairier for less-well maintained packages; for another example, see [https://groups.google.com/d/msg/idris-lang/h2uWYmqHcc0/5k0jNmQ3BAAJ this thread] about installing Idris (another programming language, written in Haskell), where one had to use both {{ic|--allow-newer}} and {{ic|1=--constraint='haskeline < 0.8.0.0'}} command-line flags to get a successful compile.

==== Removing packages ====

There is no easy way to do it. Cabal does not have support for this functionality but there are external tools like [https://github.com/phadej/cabal-extras#cabal-store-gc cabal-store-gc].

To reinstall the entire user-wide Haskell package system, remove {{ic|~/.cabal}} and {{ic|~/.ghc}} and start from scratch. This is often necessary when GHC is upgraded.

For more precision, it is possible to use {{ic|ghc-pkg unregister ''package''}} or {{ic|ghc-pkg hide ''package''}}/{{ic|ghc-pkg expose ''package''}} directly on the [https://downloads.haskell.org/ghc/8.10.2/docs/html/users_guide/packages.html#package-databases user package database] — this makes GHC "forget" about an installed package (or pretend it is not there). However neither of these removes any files.

=== Stack ===

Stack is another tool to manage Haskell packages. It has slightly different goals than Cabal, with a slightly different philosophy. It uses Cabal library under the hood and integrates with Hackage — but maintains its own repositories of packages (snapshots) on Stackage with the promise that snapshots are curated and include packages which work well together.

==== Installing packages ====

In its default configuration, Stack installs compiled executables to {{ic|~/.local/bin}}. Add this directory to the {{ic|$PATH}} environment variable in your shell configuration file, for instance {{ic|~/.bashrc}} for {{Pkg|bash}} or {{ic|~/.zshrc}} for {{Pkg|zsh}}:

 export PATH="$HOME/.local/bin:$PATH"

Run the following command to download, build and install a Stackage package:

 stack install ''package''

{{Warning|As of December 2024 Stack [https://github.com/commercialhaskell/stack/issues/3409 ignores] {{ic|ghc-options}} from {{ic|~/.stack/config.yaml}} while building {{ic|Setup.hs}}. If you experience build errors in {{ic|Setup.hs}} like {{ic|Could not find module ‘Prelude’ There are files missing in the ‘base-...’ package}}, try to install {{Pkg|ghc-static}} package as a workaround.}}

You can also build and install a Haskell package from source by running the following command from the package directory:

 stack install --resolver ''resolver''

Note that you should specify the same resolver as one used for {{ic|stack setup}} command.

==== Removing packages ====

Stack does not support the "uninstall" operation.

If you want to reinstall the entire user-wide Haskell package system, remove {{ic|~/.stack}} directory and start from scratch. This is often necessary when GHC is upgraded.

== Development tools ==

=== Tools ===

==== haskell-language-server ====

[https://github.com/haskell/haskell-language-server haskell-language-server] is a [https://microsoft.github.io/language-server-protocol Language Server Protocol] (LSP) implementation for Haskell. It provides IDE-like features such as code completion, "goto definition", documentation on hover, linting, formatting or refactoring for any editor integrating with the LSP.

If you are using dynamically linked Haskell packages from [[pacman]], install {{Pkg|haskell-language-server}}. Otherwise, if you prefer static linking, install {{AUR|haskell-language-server-static}}. This package contains statically linked binaries for each supported version of GHC. Alternatively, haskell-language-server can be installed via [[#ghcup|ghcup]] or by the [https://marketplace.visualstudio.com/items?itemName=haskell.haskell Haskell extension] for [[#Visual Studio Code|Visual Studio Code]].

haskell-language-server will attempt to automatically determine the build configuration when you open your project. If automatic detection fails, you might want to [https://haskell-language-server.readthedocs.io/en/latest/configuration.html#configuring-your-project-build configure it manually] using a {{ic|hie.yaml}} file in the project root directory.

==== ghcid ====

[https://github.com/ndmitchell/ghcid ghcid] is a [https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/ghci.html GHCi]-based tool for Haskell development that provides simple and robust way to display compiler errors and warnings on every source code change. It can be installed via {{AUR|ghcid}} package.

==== hoogle ====

[https://github.com/ndmitchell/hoogle hoogle] allows you to search the Haskell libraries by either function name, or by approximate type signature. It can be installed via {{Pkg|hoogle}} package.

An online version of hoogle is available at https://hoogle.haskell.org.

=== Linters ===

==== hlint ====

[https://github.com/ndmitchell/hlint hlint] suggests possible improvements to Haskell code such as using alternative functions, simplifying code and spotting redundancies. It is available through {{Pkg|hlint}} package.

==== stan ====

[https://github.com/kowainik/stan stan] is a Haskell static analyzer, complementary to [[#hlint|hlint]]. It is in the beta phase as of June 2021.

==== weeder ====

[https://github.com/ocharles/weeder weeder] is an application to perform whole-program dead-code analysis.

=== Formatters ===

* {{App|Floskell|Fork of hindent focusing on flexibility and configurability.|https://github.com/ennocramer/floskell|{{Pkg|haskell-floskell}}}}
* {{App|Fourmolu|Fork of Ormolu that adds an ability to configure various formatting parameters.|https://github.com/parsonsmatt/fourmolu|{{Pkg|haskell-fourmolu}}}}
* {{App|hindent|Extensible Haskell pretty printer.|https://github.com/mihaimaruseac/hindent|{{Pkg|hindent}}}}
* {{App|Ormolu|Formatter for Haskell source code, implementing one "true" formatting style which admits no configuration.|https://github.com/tweag/ormolu|{{Pkg|haskell-ormolu}}}}
* {{App|stylish-haskell|Simple Haskell code prettifier.|https://github.com/jaspervdj/stylish-haskell|{{Pkg|stylish-haskell}}}}

=== Editors ===

==== Visual Studio Code ====

[[Visual Studio Code]] has a [https://marketplace.visualstudio.com/items?itemName=haskell.haskell Haskell extension] powered by [[#haskell-language-server|haskell-language-server]]. If you do not have haskell-language-server installed, the Haskell extension will automatically download and install statically linked Linux binaries for you.

==== IntelliJ IDEA ====

[https://www.jetbrains.com/idea IntelliJ IDEA] support for Haskell is provided by the [https://plugins.jetbrains.com/plugin/8258-intellij-haskell Haskell plugin]{{Dead link|2024|12|15|status=404}}. It works with any edition of IntelliJ IDEA including {{Pkg|intellij-idea-community-edition}}.

You will need to install Stack in order to create a new project or import an existing one into IntelliJ IDEA. As of June 2021 Cabal-only projects [https://github.com/rikvdkleij/intellij-haskell/issues/625 are not supported].

==== Vim ====

Basic syntax highlighting and indentation for [[Vim]] can be obtained via the [https://github.com/neovimhaskell/haskell-vim haskell-vim] plugin. For better IDE-like experience use one of [https://vimawesome.com/?q=LSP LSP client] plugins (e.g. [https://github.com/neoclide/coc.nvim coc.nvim], [https://github.com/dense-analysis/ale ALE], [https://github.com/autozimu/LanguageClient-neovim LanguageClient-neovim]) together with [[#haskell-language-server|haskell-language-server]].

==== Emacs ====

Basic [[Emacs]] support for Haskell is provided by the official [https://github.com/haskell/haskell-mode haskell-mode]. For more advanced features, also use [https://github.com/emacs-lsp/lsp-haskell lsp-haskell] with [[#haskell-language-server|haskell-language-server]].

== Alternate installations ==

The methods described in this sections are best suited for Haskell development setups. It is possible to use them along packages from the [[official repositories]], if this is the case, make sure you know which version of the Haskell package you are using, if the one installed by [[pacman]] or by one of the following methods.

=== ghcup ===

This is the recommended method for installing Haskell in any Linux distribution. GHCup installs GHC, tools and libraries in your home directory and allows to have multiple versions in parallel and handle them with relative ease. It is similar in scope to [https://github.com/rust-lang/rustup rustup], [https://github.com/pyenv/pyenv pyenv] and [https://github.com/jenv/jenv jenv].

Install {{AUR|ghcup-hs-bin}} package. Alternatively, you may follow official [https://www.haskell.org/ghcup installation instructions] or manually download [https://downloads.haskell.org/~ghcup ghcup binary] and place it somewhere into your {{ic|$PATH}}.

By default, ghcup will install executables into {{ic|~/.ghcup/bin}}. You need to add this directory to the {{ic|$PATH}} environment variable in your shell configuration file, for instance {{ic|~/.bashrc}} for {{Pkg|bash}} or {{ic|~/.zshrc}} for {{Pkg|zsh}}. If you want to run executables installed by Cabal, add {{ic|~/.cabal/bin}} to {{ic|$PATH}} as well:

 export PATH="$HOME/.cabal/bin:$HOME/.ghcup/bin:$PATH"

{{Tip|If you want to use XDG style directories, define the {{ic|GHCUP_USE_XDG_DIRS}} environment variable (https://ghcup.readthedocs.io/en/latest/guide/#xdg-support).}}

GHCup provides a convenient TUI which supports most of its functionality:

 $ ghcup tui

Alternatively, you can use the following CLI commands:

List available versions of GHC and Cabal:

 $ ghcup list

Install the recommended version of GHC:

 $ ghcup install ghc

You can also install a specific version of GHC, for example:

 $ ghcup install ghc 8.10.2

The commands above do not automatically make GHC available on the {{ic|$PATH}}. You need to select which GHC version to use by default:

 $ ghcup set ghc 8.10.2

{{Note|GHCup is commonly used in combination with Cabal to manage other Haskell packages, you can use it to install Stack see [[#Stack]].}}

Install the recommended version of Cabal:

 $ ghcup install cabal

GHCup can install [[#haskell-language-server|haskell-language-server]] too, use the following command:

 $ ghcup install hls

For more information, refer to official [https://ghcup.readthedocs.io/en/latest/guide ghcup] and [https://cabal.readthedocs.io/en/latest Cabal] documentation.

==== Using along native installation ====

In case you decide to use '''GHCup and Cabal''' along the native installation you need to specify Cabal which GHC to use specifying the path of the GHC version to use in {{ic|$HOME/.config/cabal/config}}, search for the line {{ic|with-compiler:}} and uncomment it:

  with-compiler: ''path_of_your_ghc''

Remember that the path of your GHC in case of using GHCup is going to be under {{ic|$HOME/.ghcup/bin}}. Also GHCup, once you set the GHC version you wish, will link that version to {{ic|$HOME/.ghcup/bin/ghc}}. If you set that path in the Cabal configuration, you can change which version of GHC Cabal uses using GHCup.

=== Stack ===

You can install Stack using the {{AUR|stack-bin}} package or using GHCup (see [[#ghcup]]). Alternatively, you may follow official [https://docs.haskellstack.org/en/stable/install_and_upgrade installation instructions] or manually download [https://github.com/commercialhaskell/stack/releases Stack binary] and place it somewhere into your {{ic|$PATH}}.

If you want to run executables installed by Stack, add {{ic|~/.local/bin}} directory to the {{ic|$PATH}}, see [[Environment variables]] for more information on how to do this.

Stack will use an isolated version of GHC, so it does not require any additional configuration. Run {{ic|stack setup}} to automatically install GHC from the latest Stackage LTS snapshot:

 $ stack setup

You can now use Stack to build and install statically linked Haskell packages without any special configuration or command line flags:

 $ stack install ''package''

For more information, refer to official [https://docs.haskellstack.org/en/stable Stack documentation].

=== Nix ===

{{Expansion|I cannot offer a good enough overview, due to no experience with it}}

A completely different way of installing Haskell is [[Nix]] package manager. Nix has a steeper learning curve but offers greater flexibility in managing both Haskell and non-Haskell packages in a reliable and reproducible fashion.

== Tips and tricks ==

=== Static linking ===

{{Warning|1=There is no warranty that it will work correctly, since the GHC version in the repositories is very outdated. You may face with bugs that currently have no solution other than updating GHC [https://gitlab.haskell.org/ghc/ghc/-/merge_requests/13070?commit_id=cdcc6b763b91c4cbf68eacfe2997998550ba49d0].}}

{{Note|
* This section explains how to build statically linked Haskell packages on Arch, but still use GHC installed from the official repositories. Before you proceed, make sure to remove {{ic|~/.cabal}} and {{ic|~/.stack}} directories if they exist.
* In the context of this article, static linking does not mean generating completely static ELF binaries. Only Haskell code will be linked statically into a single ELF binary, which may be dynamically linked to other system libraries such as {{Pkg|glibc}}.
}}

To use static linking, one must, at minimum, install the static boot libraries through the {{Pkg|ghc-static}} package. This would allow you to build projects that depend exclusively on the boot libraries as well as on any other libraries that are not installed through the {{ic|haskell-*}} packages from the official repositories.

Unfortunately, if your project depends on any of dynamically linked {{ic|haskell-*}} packages that you have installed, Cabal does not take the absence of static libraries into account during dependency resolution. As a result, it will try to use the existing {{ic|haskell-*}} package and then fail with [https://bugs.archlinux.org/task/54563#comment158808 linker errors] when it discovers the static libraries are missing:

 Could not find module ‘''SomePackage.SomeModule''’
 There are files missing in the ‘''somepackage-0.1.0.0''’ package,
 try running 'ghc-pkg check'.
 Use -v (or `:set -v` in ghci) to see a list of the files searched for.

Unlike {{ic|ghc-static}}, there are no "{{ic|haskell-*-static}}" packages available for linkage. There are other ways to work around this issue though, as described in each of the sections below.

==== Static global package database ====

A direct [https://www.reddit.com/r/linux/comments/9emwtu/arch_linux_ama/efjnyd6/ approach] is offered by the official {{Pkg|ghc-static}} package, which exposes an alternative "static" global package database at {{ic|/usr/lib/ghc-''version''/static-package.conf.d}}. The static database is limited to only the statically linkable boot packages, therefore if Cabal is reconfigured to use the static database instead of the default database, it would behave as though the dynamic-only {{ic|haskell-*}} packages do not exist.

The precise path of the static database could be determined at build time using a command such as:

{{hc|
$ ghc --print-global-package-db {{!}} sed 's/\(package\.conf\.d\)$/static-\1/'|
/usr/lib/ghc-''version''/static-package.conf.d
}}

Here is how to enable the static database for use:

* When building packages with Cabal, one can pass the following flag to limit the selection of global packages to only the boot packages:

 $ cabal configure --ghc-pkg-option="--global-package-db=$(ghc --print-global-package-db | sed 's/\(package\.conf\.d\)$/static-\1/')"

* When building directly using GHC rather than Cabal, one can pass the following flags to override the global package database:

 $ ghc -clear-package-db -package-db "$(ghc --print-global-package-db | sed 's/\(package\.conf\.d\)$/static-\1/')" -user-package-db ...

==== ghc-pristine ====

Install {{AUR|ghc-pristine}} package, which wraps over an existing GHC installation to create a separate GHC distribution in {{ic|/usr/share/ghc-pristine}}, with a package database that contains only boot libraries. This effectively creates a semi-isolated environment without dynamically linked {{ic|haskell-*}} packages, but still makes use of the GHC compiler from the official repositories. Then, to build software with static linking, one simply needs to invoke the wrapped compiler {{ic|/usr/share/ghc-pristine/bin/ghc}}. For Cabal, this amounts to the following configuration in {{ic|~/.cabal/config}}:

{{hc|~/.cabal/config|
with-compiler: /usr/share/ghc-pristine/bin/ghc
}}

You can also specify the path to the compiler on a per-project basis by running the following command from the project directory:

 $ cabal configure --with-compiler=/usr/share/ghc-pristine/bin/ghc

==== cabal-static ====

Another way to gain back static linking on Arch is to install {{AUR|cabal-install-bin}} package. Unlike the official {{Pkg|cabal-install}}, this one does not pull dynamically linked {{ic|haskell-*}} dependencies from the official repositories and avoids mixing static and shared Haskell libraries installed on the same system. Then you can use Cabal as usual with the following limitation: '''you have to make sure''' that the only other Haskell packages you have installed are {{Pkg|ghc}}, {{Pkg|ghc-libs}} and {{Pkg|ghc-static}} (not {{Pkg|cabal-install}}, {{Pkg|stack}} and none of the {{ic|haskell-*}} packages available in the official repositories).

==== stack-static ====

Install {{AUR|stack-bin}} package. Similarly to {{ic|cabal-static}} method, make sure that the only other Haskell packages you have installed from the official repositories are {{Pkg|ghc}}, {{Pkg|ghc-libs}} and {{Pkg|ghc-static}}. Then setup Stack to use system GHC as explained in [[#Configuring Stack for dynamic linking]]:

 $ stack setup --system-ghc --resolver ''resolver''

To make these options permanent, paste the following snippet to {{ic|~/.stack/config.yaml}}:

{{hc|~/.stack/config.yaml|
# Stop downloading GHCs into isolated locations under ~/.stack.
install-ghc: false

# Allow Stack to pick the system GHC (false by default).
system-ghc: true

# Allow to use, say, Stackage snapshot for GHC 8.8.2 with system GHC 8.8.3.
compiler-check: newer-minor
}}

This configuration will allow you to build statically linked packages as you would normally do, but using system GHC installation instead of GHC provided by Stack.

==== hpack-static-bin ====

{{AUR|hpack-static-bin}} provides a statically linked (meaning no {{ic|haskell-*}} dependencies) alternative to {{Pkg|haskell-hpack}}. It is precompiled, so no make dependencies are needed.

== See also ==

* [https://www.haskell.org Official website of the Haskell programming language]
* [https://www.haskell.org/documentation Haskell documentation]
* [https://wiki.haskell.org/Haskell Haskell Wiki]
* [https://downloads.haskell.org/ghc/latest/docs/html/users_guide GHC User Guide]
* [https://cabal.readthedocs.io/en/latest Cabal User Guide]
* [https://docs.haskellstack.org/en/stable Stack User Guide]
* [https://hackage.haskell.org Haskell community's central package archive]
* [https://www.stackage.org Stable source of Haskell packages]
* [https://hoogle.haskell.org Haskell API search engine]
* [https://learnyouahaskell.com Learn You a Haskell for Great Good!]
* [https://book.realworldhaskell.org Real World Haskell]
* [https://en.wikibooks.org/wiki/Haskell Haskell Wikibook]
* [http://dev.stephendiehl.com/hask What I Wish I Knew When Learning Haskell]
* [https://github.com/krispo/awesome-haskell Awesome Haskell: an auxiliary list of awesome Haskell links, frameworks, libraries and software]
Return to Haskell.
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