An alterantive to running GHCI

Some students are having problems installing GHCI. A work-around is to use an online version. However, this is both slower and requires you to revise how you write the code a bit.

1. Visit https://repl.it/languages/haskell
2. Enter the following code in main.hs:

   module Main where
   
   add a b = if a == b then 2 * a else a + b
   
   trials = ["Test 1: add 8 and 5: " ++ (show (add 8 5)),
             "Test 2: add -3 and 4: " ++ (show (add (-3) 4)),
             "Test 3: add 9 and 9: " ++ (show (add 9 9))]
   
   main :: IO ()
   main = putStrLn (show trials)
   

3. Click on the Run > button and confirm you get output like

           ["Test 1: add 8 and 5: 13","Test 2: add -3 and 4: 1","Test 3: add 9 and 9: 18"]
   

4. Replace the definition of add by your own functions.
5. Rewrite the trials variable to execute your code against various cases.
6. Run your code and debug as necessary.

You might also find it useful to use tuples for tests that return differen types:

        f x = x * x
        main = putStrLn(show (f 3, f (-1), f 1.2))

Just in case you're having problems, here's what I see: