[Haskell-cafe] Why there is not standard Monoid instance for ZipList a?

Vladimir Reshetnikov v.reshetnikov at gmail.com
Fri Oct 16 05:52:45 EDT 2009

I find the following instance very convenient:
import Data.Monoid
import Control.Applicative
instance Monoid a => Monoid (ZipList a) where
  mempty = pure mempty
  mappend = liftA2 mappend

Any reason why it is not in the standard library?

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