edit: misread the parent as saying the opposite of what it actually meant

> The Haskellite approach would also say that "what operations are available on that thing" is the wrong way round; you define your operation, and the type signature tells you what kind of things will work with it.

i'm not sure if i understand. using typeclasses i can define a Haskell function for summing collections:

  sum :: (Foldable f, Monoid a) => f a -> a
  sum x = foldr (<>) mempty x

and it'll work for any Foldable collection (supporting `reduce`) of Monoidal values (supporting "addition", or the `<>` operator) - lists of strings, trees of ints, etc. that sounds a lot like "define your operation, and the type signature tells you what kind of things will work with it"