Hello all, I recently (re)noticed the following duplication: base:Control.Applicative newtype Const a b = Const { getConst :: a } instance Functor (Const m) where... instance Monoid m => Applicative (Const m) where... transformers:Data.Functor.Constant newtype Constant a b = Constant { getConstant :: a } instance Functor (Constant a) where... instance Foldable (Constant a) where... instance Traversable (Constant a) where... instance (Monoid a) => Applicative (Constant a) where... I don't see any reason for this redundancy. I propose we: (1) add the Foldable and Traversable instances to base, and (2) deprecate transformers:Data.Functor.Constant This will cause breakage to any orphan instances of Foldable/Traversable for Const, but that seems fine by me. Eventually we'll want to remove transformers:Data.Functor.Constant (or have it re-export the Const stuff from base:Control.Applicative); but that can be handled later. Deadline: 14 May 2012. -- Live well, ~wren