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# Haskell package guidelines

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Reason: Please help improve this article by creating reasonable package creation guidelines for Haskell packages. (Discuss in Talk:Haskell package guidelines)

This document aims to cover standards and guidelines for producing good Haskell packages on Arch.

Until this document is written, contact User:Felixonmars.

## Package naming

For Haskell libraries, use `haskell-libraryname` usually the same name as on hackage.

Note The package name should be entirely lowercase.

## Architecture

See PKGBUILD#arch.

Every Haskell library or program is architecture-dependent.

## Source

The preferred source of a Haskell program or library is from hackage. PKGBUILD#source `source=()` array should use the following URL template:

    https://hackage.haskell.org/packages/archive/$_hkgname/$pkgver/$_hkgname-$pkgver.tar.gz

Note that a custom `_hkgname` variable is used instead of `pkgname` since Haskell packages are generally prefixed with haskell-. This variable can generically be defined as follows:

    _hkgname=stm-delay

## Creating packages

arch-hs is provided to automate `PKGBUILD` generation and maintenance.

To generate a series of `PKGBUILD`s for a Hackage package (and its unpackaged dependencies):

    $ arch-hs -o /path/to/workdir library_name

## Updating packages

Warning Haskell package upgrades require special consideration and differ significantly from other language ecosystems. If you are new to Haskell packaging, thoroughly review this section before attempting to update any package.

When a Haskell library changes its build flags or is updated, all dependent packages and their transitive dependents, including makedepends and checkdepends, need to be rebuilt. See the subsections below for determining the correct rebuild order.

Moreover, in the Haskell ecosystem, the latest releases of libraries frequently do not work together. It is therefore advisable to upgrade packages incrementally, in small steps, and read upstream changelogs to identify potential upstream issues. This holds in particular for packages with a non-negligible number of packages in their reverse dependency chain. Sometimes, an incompatibility may only be discovered during the rebuilds and may turn out to be non-trivial to fix; in such cases, it may be best to revert changes and document the incompatibility in the relevant bumpbuddy ticket.

### Identifying required changes

To compare dependencies and other packaging metadata for updating an existing package:

    $ arch-hs-diff library_name old_version new_version

To compare Arch [extra] package versions and their corresponding Hackage package versions:

    $ arch-hs-sync check

Note that `arch-hs` uses cabal-install to maintain Hackage databases, so please update your cabal-install database regularly to keep them fresh:

    $ cabal update

### Package rebuilds

The genrebuild tool can be used to find out what needs rebuilding and how.

Example usage:

    $ ./genrebuild -H haskell-basement

## PKGBUILD library example

Note It is highly recommended to use arch-hs when adding new packages. Please review the section on #Creating packages above.

Packaging a Haskell library is different from packaging a Haskell program, the libraries packaged in Arch Linux are meant to be used by packaged Haskell programs.

    PKGBUILD

    # Maintainer: Your Name <youremail@domain.com>
    _hkgname=stm-delay
    pkgname=haskell-stm-delay
    pkgver=
    pkgrel=1
    license=()
    arch=('x86_64')
    url="https://hackage.haskell.org/package/$_hkgname"
    depends=(ghc-libs)
    makedepends=(ghc)
    source=("https://hackage.haskell.org/packages/archive/$_hkgname/$pkgver/$_hkgname-$pkgver.tar.gz")
    sha256sums=()

    build() {
      cd "$_hkgname-$pkgver"

      runhaskell Setup configure -O --enable-shared --enable-debug-info --enable-executable-dynamic --disable-library-vanilla \
        --prefix=/usr --docdir="/usr/share/doc/$pkgname" --datasubdir=$pkgname --enable-tests \
        --dynlibdir=/usr/lib --libsubdir=\$compiler/site-local/\$pkgid \
        --ghc-option=-optl-Wl\,-z\,relro\,-z\,now \
        --ghc-option='-pie'

      runhaskell Setup build $MAKEFLAGS
      runhaskell Setup register --gen-script
      runhaskell Setup unregister --gen-script
      sed -i -r -e "s|ghc-pkg.*update[^ ]* |&'--force' |" register.sh
      sed -i -r -e "s|ghc-pkg.*unregister[^ ]* |&'--force' |" unregister.sh
    }

    check() {
      cd "$_hkgname-$pkgver"
      runhaskell Setup test
    }

    package() {
      cd "$_hkgname-$pkgver"

      install -D -m744 register.sh "$pkgdir/usr/share/haskell/register/$pkgname.sh"
      install -D -m744 unregister.sh "$pkgdir/usr/share/haskell/unregister/$pkgname.sh"
      runhaskell Setup copy --destdir="$pkgdir"
      install -D -m644 "LICENSE" "${pkgdir}/usr/share/licenses/${pkgname}/LICENSE"
      rm -f "${pkgdir}/usr/share/doc/${pkgname}/LICENSE"
    }

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