+-- | The 'Maybe' type encapsulates an optional value. A value of type
+-- @'Maybe' a@ either contains a value of type @a@ (represented as @'Just' a@),
+-- or it is empty (represented as 'Nothing'). Using 'Maybe' is a good way to
+-- deal with errors or exceptional cases without resorting to drastic
+-- measures such as 'error'.
+--
+-- The 'Maybe' type is also a monad. It is a simple kind of error
+-- monad, where all errors are represented by 'Nothing'. A richer
+-- error monad can be built using the 'Data.Either.Either' type.
+
+data Maybe a = Nothing | Just a
+ deriving (Eq, Ord)