School of Haskell

A guided tour through BiteMyApp's comprehensive Haskell tutorial.

Installing Haskell

For those just getting started, follow these steps to install the latest version of GHC. For those using OSX, the recommend package manager is Homebrew. For those using other OS's, replace brew install with your own package manager in any following shell commands (lines prefixed by a $).

1. Install GHC (the Haskell compiler) and Cabal (the Haskell package manager)

   $ brew install ghc cabal-install
   

2. Add $HOME/.cabal/bin to your shell's $PATH variable

3. Install only the Haskell modules required globally. Everything else will be installed in project-specific sandboxes.

   $ cabal update
   $ cabal install hspec
   

Enabling a great Haskell toolset (using Vim)

Part of what makes Haskell so fantastic is the tooling that can be built around a compiler that can infer so much about its programs. These instructions are for those using Vim, but similar instructions should be available for Emacs or other text editors.

1. Install GHC-mod

   $ cabal install happy
   $ cabal install ghc-mod
   

2. Install the GHC-mod plugin for Vim. If you are inexperienced with installing Vim plugins, I recommend using Vundle.

3. (Optional) Add shortcut keys for the GHC-mod commands. Mine are listed below, which can be listed in your $HOME/.vimrc file.

   au FileType haskell nnoremap <buffer> <Leader>ht :GhcModType<CR>
   au FileType haskell nnoremap <buffer> <Leader>hh :GhcModTypeClear<CR>
   au FileType haskell nnoremap <buffer> <Leader>hc :GhcModCheck<CR>
   au FileType haskell nnoremap <buffer> <Leader>hl :GhcModLint<CR>

NOTE: If you've installed GHC via a package manager, you're probably using version 7.8.4 or less (which you can check via $ ghc --version. If so, you must use Cabal version 1.20.0.6 or less for ghc-mod to function properly. You may force the Cabal version via $ cabal install cabal-install-1.20.0.6.

Beginning a homework assignment

Before beginning a homework, you should:

1. Branch this project

   $ git branch [an appropriate branch name for the homework]
   

2. Initialize a Cabal sandbox in the current homework directory and install any required packages. For example:

   $ cd cis194/homework-1
   $ cabal sandbox init
   $ cabal install --only-dependencies --enable-tests
   $ cabal configure --enable-tests
   

3. Run the specs to ensure they fail

   $ cabal test --show-details=always --test-options="--color"
   

You're now ready to begin replacing the undefined functions with actual function definitions. Running and passing the specs as you write functions will ensure that your later work is built upon previous correct work.

Discovering functions

Haskell doesn't come packaged with a standard library as do many other languages. Instead, it has the Haskell Platform—a collection of curated packages deemed most useful and of high quality. While it's not recommended that you install the platform per se, I do recommend that you consult the Haskell Platform documentation as your first place to discover new libraries and functions and install the libraries as needed.

Another great way to discover functions is via Hoogle, the Haskell function search engine. With Hoogle, functions may be discovered by name or type signature.