Instructions for installing Haskell

These instructions are for GHC 7.8.4, and will be kept up to date to the latest released version of GHC.

Why does this set of instructions exist?

Why this set of instructions about how to install Haskell on your computer? Isn't the official site for Haskell sufficient?

Sadly, right now (January 2015), the answer is no, for unfortunate reasons that newcomers should not have had to deal with when getting started. The Haskell community is working to improve the setup process. The official download page is still confusing, so I have created a consistent setup process that I feel is best.

I have personally created Haskell setups on Mac OS X, Windows, and Linux (Ubuntu), and have created the following instructions for these platforms.

Understanding the fully set up environment

Before following the instructions below, it may be helpful to first understand, at a high level, the end goal of the installation process:

• Install the right version of GHC, the de facto standard native compiler and interpreter.
• Install the right version of cabal-install, the tool for building and packaging in accordance with the protocols required by the Cabal library that will come with your GHC. The cabal-install executable (hereafter called cabal, as it is on the command line) is implemented in Haskell.
• Initialize use of the cabal executable, letting it create a directory .cabal in your home directory and download the list of packages from Hackage, the standard Haskell community package archive.
• Install, using cabal, some auxiliary tools, Happy and Alex, which are needed for cabal to build and install some packages.

Instructions

Clean up old stuff first!

If you have old versions of GHC or Cabal installed, you should remove them. We want to install ghc-7.8.3 or ghc-7.8.4, and something in the range of cabal-1.20 to cabal-1.22.

Check your versions:

ghc --version
cabal --version

Also, if you have old directories created from old versions of GHC or Cabal, wipe out your home directory's repositories:

rm -rf ~/.ghc
rm -rf ~/.cabal

This will enable a clean process the next time you use the newer version of Cabal you have installed.

Mac OS X

I recommend using Homebrew if on a Mac post-Lion, in order to get GHC 7.8.4.

First, make sure that you have XCode command line tools installed (else weird errors happen):

$ brew --config | grep CLT
CLT: 6.1.1.0.1.1416017670

If you have

CLT: N/A

you need to run

xcode-select --install

After verifying that you have XCode command line tools installed, proceed:

brew install ghc
brew install cabal-install
cabal update
cabal install alex happy

Then, in your shell startup file, add $HOME/.cabal/bin to your PATH, e.g., in my $HOME/.zshrc I have

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

Restart your terminal and you're ready to go.

Windows

A Windows installer is available at minghc.

There are 32-bit and 64-bit installers, e.g., for the latest 64-bit version, download and run the installer for GHC 7.8.4, 64-bit. This installer also includes pre-built Alex and Happy, so all you have to do is go to a command window and do

cabal update

Linux

Full Linux instructions are here. Currently, the instructions are for GHC 7.8.3, but 7.8.4 has been out.

For Ubuntu, for example, do

sudo apt-get update
sudo apt-get install -y software-properties-common
sudo add-apt-repository -y ppa:hvr/ghc
sudo apt-get update
sudo apt-get install -y cabal-install-1.22 ghc-7.8.4
cat >> ~/.bashrc <<EOF
export PATH=~/.cabal/bin:/opt/cabal/1.22/bin:/opt/ghc/7.8.4/bin:$PATH
EOF
export PATH=~/.cabal/bin:/opt/cabal/1.22/bin:/opt/ghc/7.8.4/bin:$PATH
cabal update
cabal install alex happy

Final required step: testing your installation

Since we want to be writing and running tests immediately ("test-driven learning"?), we want to install doctest, hspec, and quickcheck. One great way to do this and verify that your installation is working is to try to run a successful build and test of an excellent starter Haskell project, unit-test-example:

git clone https://github.com/kazu-yamamoto/unit-test-example
cd unit-test-example
cabal install --enable-tests --only-dependencies
cabal configure --enable-tests
cabal build
cabal test

Note that the cabal install command will install the dependencies found in the unit-test-example.cabal file. Ideally, you should run this before the workshop, to save on a flood of WiFi access on site to pull down and build dependencies there.

Your setup is complete for the workshop when cabal test succeeds.

If you want to jump ahead before the workshop, you can look at an explanation of what this process does, in the provided tutorial.

Questions?

If you have any questions or corrections, please open a GitHub issue or submit a pull request!