u/edwardkmettin r/haskell • Recommends
On “Missing the point of applicatives”
ZipList can't be extended compatibly to a `Monad`.
Validation, can't be extended compatibly to a `Monad` and lets you extract _multiple_ errors not just one.
Concurrently can't be extended compatibly to a `Monad` but lets you run a number of computations in parallel. (There is a `Monad` instance that is broken, but it is being removed.)
Notably, you know the issue with how arbitrary monads don't compose and so you need transformers to hack around this? Well, Applicatives do:
instance (Applicative f, Applicative g)
=> Applicative (Compose f g)
We can make parsers that take advantage of the limitations of `Applicative` to parse more efficiently, even if they do extend to become…