I was thinking of things like monads. They’re a class of type constructors with a couple of associated functions (unit & bind or unit & join). The definition is undoubtedly simple, as well as fundamental in Haskell. But understanding how to use them, what to use them for, how to tell whether & why a type admits monad/applicative/functor instances, &c., are still difficult things for a lot of people, because these are unfamiliar abstractions. Moreover, they take advantage of unfamiliar features like higher-kinded types, so you can’t even explain them by offering a translation to other languages, because most other languages lack the ability to adequately express them.
For myself, I think of learning as “discovering simplicity”. I know I understand something when it finally feels as simple as it really is.
I was thinking of things like monads. They’re a class of type constructors with a couple of associated functions (unit & bind or unit & join). The definition is undoubtedly simple, as well as fundamental in Haskell. But understanding how to use them, what to use them for, how to tell whether & why a type admits monad/applicative/functor instances, &c., are still difficult things for a lot of people, because these are unfamiliar abstractions. Moreover, they take advantage of unfamiliar features like higher-kinded types, so you can’t even explain them by offering a translation to other languages, because most other languages lack the ability to adequately express them.
For myself, I think of learning as “discovering simplicity”. I know I understand something when it finally feels as simple as it really is.