Jon Pretty

Or maybe, Scala *does* make it easy to abstract over monad-like types (as Cats, Scalaz, Mercator, ... shows), but there are no monad/functor/... typeclasses in stdlib?

It's the abstracting over that's the problem for Scala, rather than the use (which is great when the type is concretely known)... the main problem is that for-comprehensions allow more general types than can be easily represented by an OOP-style typeclass interface...

Adding a F[_]: Monad type constraint and a cats.implicits._ import, or defining the instance by implementing a trait is easy enough. The problem is there’s no standard way to do this, so libraries roll their (incompatible) own, or just avoid altogether

I think part of the problem is that a dependency on the whole of Cats or Scalaz, if all you want is a way to abstract over monad-like things, is too much... which is why people roll their own...

This might be only a psychological barrier, I suspect cats might be one od the smaller dependencies (measuring in bytes). And no transitive ones, too

FWIW neither cats nor scalaz are very small. Last time I checked cats-core was something about 8mb, I suspect due to generated code

it says 4mb here https://mvnrepository.com/artifact/org.typelevel/cats-core_2.12/1.2.0 …

Ah, I am mistaken then, thanks for checking :) it's still more than I initially thought