Please go to the Haskell Wikibook (https://en.wikibooks.org/wiki/Haskell) and
study the following sections for a start on very basic Haskell and basic usage
of ghci (Haskell REPL):

Under "Beginner's Track", under "Haskell Basics":
  from "Getting set up"
  to and including "Type basics"


Normally you would not write code at the ghci prompt directly (can be done but
doesn't scale).  Use your favourite editor to put code in a file, then go to
ghci and use its ":load" command or ":reload", then test as you like.


In case a lab computer says "Command 'ghci' not found", the full path is:

    /usr/local/cms/ghc-8.6.3/bin/ghci

(If you run into this problem, please email Albert the hostname of the lab computer.)


And then, my test file uses an extra library "HUnit" (cf. "import Test.HUnit").
You have to install it manually once (good for the whole term):

    cabal v1-update
    cabal v1-install HUnit

(cabal's full path: /usr/local/bin/cabal)

After the course, if you want to delete it to reclaim space, look under
$HOME/.cabal and $HOME/.ghc