Jon Pretty

Stop using, opt match { case Some(x) => f(x); case None => y } Stop using, http://opt.map (f).getOrElse(y) Use, opt.fold(y)(f) I feel like I'm very late to this party.

I actually kind of disagree. map(f).getOrElse(y) clearly conveys the intent of your code and makes it easy to understand for other people. fold(y)(f) doesn't. In my case at least, I always have to do the mental gymnastic of "oh, this means map.getOrElse"

But wouldn't you say that map...getOrElse is itself halfway between the pattern-match to the fold in terms of clarity? I think the difference is that right now we're much more familiar with maps than folds, especially when the context is an Option.

Honest question though: is that a proper fold? In my mind, fold is heavily linked to monoids: - takes an "empty" value - takes a merge function that's basically a monoidal append This is not what Option.fold does. Am I misunderstanding what fold is?

Your mixing `Foldable` (the typeclass) with the algebraic fold, the later is basically isomorphic to pattern matching. The fact that folding on a List is recursive, is incidental (because the type itself is recursive), not the opposite.