I'm also a fan of "imperative shell, functional core, imperative implementation of that core," where within a function that you promise to have no side effects or very specific side effects (say, a component's render function, or a transformation from one complex data representation to another), you should still feel free to use loops, imperative-style control flow, even network requests, etc. I find this puts folks used to "imperative everything" at ease, while still maintaining almost all of the benefits of functional-core provided that execution is scheduled properly.