CSE 341 - Programming Languages - Winter 2009

Running Haskell

We're using the Glasgow Haskell Compiler in 341, version 6.8.3. (GHC is the de facto standard version of Haskell.)

On CSE Undergrad Linux Machines (attu and individual machines)

At the command prompt type ghci to start it, or ghic myfile.hs to start it and load myfile.hs.

If you know your way around basic Linux commands (or are willing to learn), the lab Linux machines are the best place to run Haskell. We've got the emacs Haskell mode package already downloaded, as well as the unit test package.

Also see Using Linux and Emacs in CSE 341.

On the CSE Undergrad Windows Machines

Start Haskell via the "Start" menu. It's here:
Programs / DEV TOOLS & LANGUAGES / GHC (Haskell) / 6.8.3 / GHCI

There are also local copies of documentation under
Programs / DEV TOOLS & LANGUAGES / GHC (Haskell) / 6.8.3

You can also run Haskell on a .hs file by double-clicking on the file name, or by typing ghci or ghci MyFile.hs at the DOS command prompt.

On a Personal Machine

Haskell is available for Windows, Mac, Linux -- see the download page at http://haskell.org/ghc/download_ghc_683.html. A newer version than 6.8.3 recently came out, but since 6.8.3 works fine and is what is installed on the undergrad lab machines, that will be the official version for this offering of 341. The newer version will probably work OK as well.

Basic Haskell Commands

A few essential commands:

• :? -- list commands
• :quit
• :load [filename]
• :reload -- reload the current file set after you'ved edited it
• :cd -- change to another directory
• :type [expr] -- give the type of an expression (or -- just :t)
• :set +t tell Haskell to print type information after evaluation

If you just want to try Haskell without loading any files, just start it up. For anything interesting, though, you'll want to have a file with defintions in it. A simple way to do this is to use your favorite editor to create a file (with the extension .hs) in your home directory or a subdirectory. Save the file but leave the editor open on it. Then start up Haskell, use the :cd command to change to your home directory or subdirectory, then the :load command to load the file. Try things out. If you want to edit your file, do so and save it, and then back in Haskell reload the file using :reload.

The above directions may be all you want for 341; and in any case I'd suggest starting out that way. For students comfortable with emacs (or who are willing to learn) running Haskell from emacs is more convenient in the long run. There are directions for installing and running this at Haskell mode for Emacs.

If you are running on the ugrad linux machines, we've got the emacs Haskell mode packages downloaded already. Just add the following line to the .emacs file in your home directory:

(load "/cse/courses/cse341/common/haskell-mode-2.4/haskell-site-file")

Beware the Evil Tab!

Unlike most programming languages, whitespace is significant in Haskell. So that you can see whether things are lining up properly use a fixed-pitch font when editing. Haskell has some rule about how tabs are processed, but I recommend that you avoid tabs in Haskell code and always use spaces instead.

For emacs, if you use the Haskell mode for Emacs, it will avoid using tabs in files. Otherwise, by default, Emacs inserts tabs in place of multiple spaces when it formats a region. Putting the following in your .emacs file turns this off:

     (setq-default indent-tabs-mode nil)