When deeply nested libraries generate PRNGs, all that layering becomes impure and must be treated like any other stateful or IO code. In Haskell, that typically means living with a monad transformer or effect system managing the whole stack, and relatively little pure code remains.
The messiness gets worse when libraries use different conventions to manage their PRNG statefulness. This is a non-issue in most languages but a mess in a 100% pure setting.
