Difference between revisions of "Haskell"

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(Pros/Cons of the different methods: table for pros/cons)
(Managing Haskell packages: Link directly to the ArchHaskell page)
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The recommended workflow is the following:
 
The recommended workflow is the following:
* [[Official repositories]] or [[#ArchHaskell repository|ArchHaskell repository]] as principal source of Haskell packages (the ''or'' is exclusive here)
+
* [[Official repositories]] or [[ArchHaskell|ArchHaskell repository]] as principal source of Haskell packages (the ''or'' is exclusive here)
 
* [[#cabal-install|cabal-install]] (possibly with sandboxes) for Haskell development
 
* [[#cabal-install|cabal-install]] (possibly with sandboxes) for Haskell development
 
* [[Arch User Repository]] for packages that are not available elsewhere
 
* [[Arch User Repository]] for packages that are not available elsewhere

Revision as of 14:49, 29 August 2014

Haskell is a general purpose, purely functional, programming language.

Installation

Haskell generates machine code that can be run natively on Linux. There is nothing special required to run a binary (already compiled) software, like the ones provided in the official repositories or by the ArchHaskell group. On the other side, AUR packages or source codes requires a compiler to build the software.

Installing the compiler alone permits to build Haskell source code. For development there is a Haskell-Platform bundle which offers the complete set of tools to get started with Haskell.

Compiler

To build a Haskell source–code into native–code, a compiler must be installed. There are several implementations available, but the most used one (which became de facto the reference) is the GHC (Glasgow Haskell Compiler). It is available in the official repositories as ghc.

You can try it with the following file:

Main.hs
main = putStrLn "Hello, World"

and by running:

$ ghc Main.hs
$ ./Main 
Hello, World

Haskell platform

To start developing in Haskell easily, there is a haskell-platform bundle which is described as:

The easiest way to get started with programming Haskell. It comes with all you need to get up and running. Think of it as "Haskell: batteries included".

An AUR package exists (haskell-platformAUR), but can advantageously be replaced by installing the following packages from the official repositories:

  • ghc (ghc) — The compiler
  • cabal-install (cabal-install) — A command line interface for Cabal and Hackage
  • haddock (haddock) — Tools for generating documentation
  • happy (happy) — Parser generator
  • alex (alex) — Lexical analyzer generator

Managing Haskell packages

There are a lot of Haskell libraries and executables grouped in packages. They are all available on Hackage. To install and manage these packages, several methods are available and unusual ones are explained in the rest of this section.

The recommended workflow is the following:

cblrepo is a tool used for maintaining Haskell packages for Linux distributions. A wrapper around this, cabal2pkgbuild-gitAUR, can create PKGBUILD files from Hackage packages. See Haskell Package Guidelines for more information on creating new Haskell packages.

Pros/Cons of the different methods

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

Method Pros Cons
Official Repositories Provided by ArchLinux developers, consistent versions of packages, already compiled Only a few packages available
ArchHaskell repository Provided by ArchHaskell group, consistent versions of packages, already compiled Need manual intervention to get started with
cabal-install All packages available Installed in home folder, cabal-install is not a package manager, incompatible versions of packages possible (aka. cabal hell)
Arch User Repository Simple to get started Risk of unmaintained or orphaned packages, incompatible versions of packages possible

ArchHaskell repository

See ArchHaskell for details.

cabal-install

Warning: Discouraged method, keep in mind that cabal-install is not a package manager.
Note: The only exception is for Haskell development, where cabal-install is the recommended tool. Since version 1.18, cabal provides a sandbox system that permits to isolate different versions of libraries for different projects. There is an introduction to cabal sandbox here.

Preparation

Install cabal-install from the official repositories.

To run installed executables without specifying the path, the cabal binary folder ~/.cabal/bin must be added to the $PATH variable. That can be done by putting the following line in your shell configuration file, for instance ~/.bashrc for bash or ~/.zshrc for zsh:

PATH=$PATH:~/.cabal/bin

Installing packages

$ cabal update
$ cabal install <pkg>

You can add -j for parallel compilation. It is also possible to install a package system–wide with the --global flag, but this is strongly discouraged. With the user–wide install, all files are kept in ~/.cabal and libraries are registered to ~/.ghc, offering the possibility to do a clean-up easily by simply removing these folders. With system–wide install, the files will be dispersed in the file system and difficult to manage.

Removing packages

There is no easy way to do it.