Implementation of a type constructor for multisets, with an empty constructor and the common operators for working on multisets.
This implementation is an instance of the type classes Eq and Foldable and provides an operator mapMSet that emulates fmap, but impose an additional constraint on the output type, so it is not a Functor.
The test file exploits IO Monads for reading and writing files, computing the count of the C.I.A.O. (Characters In Alphabetical Order) of each word.