Data sources often contain incomplete and unexpected data. One common approach to parsing such data in Haskell is using the Maybe data type.

Imagine designing a function to find the nth element in a list of characters. A naïve implementation may have the type Int -> [Char] -> Char. However, if the function is trying to access an index out of bounds, we should try to indicate that an error has occurred.

A common way to deal with these errors is by encapsulating the output Char into a Maybe context. Having the type Int -> [Char] -> Maybe Char allows for some better error handling. The constructors for Maybe are Just a or Nothing, which will become apparent by running GHCi and testing out the following commands:

$ ghci

Prelude> :type Just 'c'
Just 'c' :: Maybe Char

Prelude> :type Nothing
Nothing :: Maybe a

We will set each field as a Maybe data type so that whenever a field cannot be parsed, it will simply be represented as Nothing....