The RATH project strives to provide Haskell libraries for relation-algebraic treatment of relations and related structures, and for explorations in the meta-theory of relation algebras and related abstractions.
Data.Mapin Haskell do not give rise to a category: On infinite types, like
Integer, there is no identity, which would have to be a total map of type
Map Integer Integer
An appropriate mathematical generalisation of categories are semigroupoids; I am currently working on a library of semigroupoid interfaces to relational datatypes in Haskell, see [Kahl-2006a_Semigroupoids].