This core library is (was) shipped with the Glasgow Haskell Compiler and provides a basic interface for (splittable) random number generators.
The API documentation can be found here:
http://www.haskell.org/ghc/docs/7.6.2/html/libraries/haskell98-2.0.0.2/Random.html
A module supplying this interface is required for Haskell 98.