This library defines several versions of an existential type 'Some', which works like this datastructure:
data Some f where
Some :: f a -> Some f
and operations to work with it.
However, due to GHC issue #1965, the direct implementation of this datastructure is less efficient than it could be. As a result, this library uses a more complex approach that implements it as a newtype, so there's no runtime overhead associated with wrapping and unwrapping Some values.
To use the recommended implementation, import Data.Some. If you need to ensure that you are definitely using the newtype implementation, import Data.Some.Newtype. By default, these are the same, but this can be changed via a Cabal flag.