Here's the thing that the immutable folks get absolutely right: Constrain your state space or die. So FP fits pretty much every place it helps you do that.
Even in embedded systems, is it useful to have functions that don't depend on state? Can they simplify design, reasoning, and testability? Certainly.
So even in the domains I mentioned, you can do FP to the extent that the problem domain allows, and benefit from the smaller state space. My quarrel is with the "you must use it everywhere or you're just an ignorant heathen" zealots, not with FP itself.
I have no opinion at this time. The web page didn't show me very much - it has Haskell syntax, OK; it won't cons on you all the time, good; it intends to be useful for systems programming, well and good. That's fine for the intent.
I'd want to know a bit about how it held up in practice before I gave a real opinion, and I don't know anything about that at present.
In my opinion/experience, functional programming is great for web applications. However, I believe it is much more generally applicable than AnimalMuppet.
Even in embedded systems, is it useful to have functions that don't depend on state? Can they simplify design, reasoning, and testability? Certainly.
So even in the domains I mentioned, you can do FP to the extent that the problem domain allows, and benefit from the smaller state space. My quarrel is with the "you must use it everywhere or you're just an ignorant heathen" zealots, not with FP itself.