> I'd say most of the time, you just failed to capture the commonalities. More specifically, you seek generality through exhaustiveness, when you should use genericness instead.

THIS is one of the most important things I've ever learned from programming Haskell[0]. The way to make things generic is to whittle away all of the sharp edges and implement them as compositions atop base patterns. Those base patterns arise out of polymorphism, not exhaustiveness.

You don't make lists generic by realizing that you need a list type to have all the properties of a string, a tree, a vector... You make it generic by realizing that much of its structure arises by forgetting what's inside.

[0] Which is not to say you can't learn it elsewhere, or that you cannot do it elsewhere. Instead, Haskell has the facility, the philosophy, and the community to do it really effectively all the time and so if you read Haskell code you'll be floored by some of the great examples possible there.