I have been out of my cage phase with typed functional programming for a while now¹ but there is a thing I still end up thinking about a lot (just now: because of doing some tweaks to my static site generator and using True Myth’s Maybe): The combination of a Maybe type and associated functions to work with them are just so much more general than special-case null-handling syntax like the optional chaining ?. or nullish coalescing ??, etc. operators which JavaScript, C#, and many other languages have sprouted over the past few years.

That generality is true in at least two ways, one of which gets commented on a lot in the things I read, and one of which does not. The one which gets commented on a lot is the way that map() is the same basic operation whether it’s Maybe or Array or Task or something else: functors! applicatives! monads! category theory!

The one that gets commented on less is that a type with function operating over it is just plain more useful. I built a little function² for my static site generator today which did some string handling, and where I ultimately ended up using True Myth’s Maybe type. I implemented it initially with a “null object” pattern: just returning an empty string for the case where its arguments did not have a sensible expansion. It was annoying to work with in different contexts, though; and so was returning null, which I also tried. Just returning a Maybe<string> instead of doing either a null return or a '' “default case” return let me just .map() over the result and do different things in different contexts as appropriate, though. That was impossible with '' and difficult with null, even with nullish coalescing or optional chaining, because the subsequent operations were shaped like functions, and the syntax doesn’t help with that.

It turns out that functions and types compose really nicely in a way that dedicated syntax does not (necessarily). This does not mean that dedicated syntax is bad — Lisp notwithstanding — so much as that specialization and generality do actually sit in tension with each other.