Errors and exception handling

We have been looking at Maybe and Either in earlier recipes and used them for conveying error. For example, Nothing :: Maybe a conveys that the evaluation has resulted in an error, and that is how we now have Nothing. Either is more informative than Maybe and conveys more information through its Left constructor.

In this recipe, we will work with three situations: 

• Working with error and catching it later
• Working with IO exception and catching it
• Creating a custom exception, raising it, and catching it

How to do it...

1. Create a new project exceptions with the simple Stack template.
2. Open src/Main.hs and edit it.
3. After the module declaration, add the following imports for Exception and for doing IO:

        import qualified Control.Exception as E
        import System.IO

4. We will write a function div1 to divide one integer by another. However, when we encounter the division by zero situation, we use the error :: String -> a function to raise an error. This function takes...