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

[Vladimir Reshetnikov]

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?

Thanks,
Vladimir
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