[sync13298]

> Every useful program ever written takes inputs and produces outputs. The interesting part is what you actually do in the middle to transforms inputs -> outputs. And that can be entirely functional.

My work needs pseudorandom numbers throughout the big middle, for example, drawing samples from probability distributions and running randomized algorithms. That's pretty messy in a FP setting, particularly when the PRNGs get generated within deeply nested libraries.

[zelphirkalt]

At what point does this get messy?

[sync13298]

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.

[zelphirkalt]

What I don't understand about your comment is: Where do these "deeply nested libraries" come from? I use one library or even std library and pass the RNG along in function arguments or as a parameter. Why would there be "deeply nested" libraries? Is it like that in Haskell or something? Perhaps we are using different definitions of "library"?

[creata]

It's not that bad if you're using a splittable RNG, is it? Any function that (transitively) depends on an RNG needs an extra input, but that's it.