Due to the nature of the Applicative https://hackage.haskell.org/package/base-4.12.0.0/docs/Control-Applicative.h... and Alternative https://hackage.haskell.org/package/base-4.12.0.0/docs/Control-Applicative.h... abstractions, they are prone to memory leaks and not as efficient as their monadic counterparts. Although all the combinators we provide in this module are perfectly expressible in terms of Applicative https://hackage.haskell.org/package/base-4.12.0.0/docs/Control-Applicative.h... and Alternative https://hackage.haskell.org/package/base-4.12.0.0/docs/Control-Applicative.h...,
Hi! Regarding the "there can be no instance for which mapM is more efficient than traverse": There have been issues with Applicative functions leaking memory where Monad ones aren't in Polysemy - some of these have been fixed, but it's not clear that there are none left. There is also this claim in parser-combinators https://hackage.haskell.org/package/parser-combinators-1.2.1/docs/Control-Ap... : please prefer Control.Monad.Combinators https://hackage.haskell.org/package/parser-combinators-1.2.1/docs/Control-Mo... instead when possible. I have not verified it, but it is a bit worrying. Personally I would love to know of some kind of reasoning regarding these things, as I'm not aware of any! (efficiency of Applicative vs Monad based functions) ====== Georgi