"Regular" functional programming is fine, mostly it's just "apply a function to a list of values" (things like fold, which seems like reduce, is a bit more involved, but not much).

It's the "factorial in recursive style" type of stuff that trips me up. I can read imperative code like I would read a book: I just do (assuming I'm familiar with the language), but this sort of recursive stuff just trips me up, never mind actually writing it.