Ask HN: Idiomatic functional programming algorithms/examples/micro-projects?

If I want to try out or demonstrate an imperative programming language I'll typically start with hello world, then some math, then some basic algorithms like maybe a sort, then some classical data structures and more advanced classical algorithms, then maybe some kind of stateful app.

I feel like there are huge bodies of algorithms, programming problems and their solutions, etc. for the imperative style, but it seems like there's less of that for the pure-functional style.

Does anyone have good resources for "idiomatic functional-programming snippets" that could be used to demonstrate or test out a language?