Denis Moskvin writes:

Is there any rationale for coexistence of

newtype Const a b = Const { getConst :: a }

from Control.Applicative and

newtype Constant a b = Constant { getConstant :: a }

from Data.Functor.Constant (transformers package)?

It was an accident. I think it would make sense to either move Constant to Control.Applicative or hide Const.