Sparse Set
Sparse Sets are useful when you have a lot of potential keys but only a small part of them is used. Sparse sets can deal with many keys while providing fast iteration over the values within the set.
There are 4 variants:
Boxed: The standard version which can deal with arbitrary Haskell values.Storable: Can only deal with Storable values.Unboxed: Can only deal with Unbox(vector package) values.NoComponent: Contains no values, only the keys.