both

Like Maybe, but with a different Monoid instance.

https://github.com/barrucadu/both

Version on this page:0.1.1.1
LTS Haskell 19.33:0.1.1.2
Stackage Nightly 2022-03-17:0.1.1.2
Latest on Hackage:0.1.1.2

See all snapshots both appears in

MIT licensed by Michael Walker
Maintained by [email protected]
This version can be pinned in stack with:both-0.1.1.1@sha256:2b661bbfdd5eea6d8926c5306c36b8bd02157227bc86eeb4aa859061f538fbc8,1654

Module documentation for 0.1.1.1

Depends on 3 packages(full list with versions):
base, semigroups, zero

The Monoid instance for Maybe behaves like so:

instance Monoid a => Monoid (Maybe a) where
  mappend (Just x) (Just y) = Just $ x <> y
  mappend (Just x) Nothing  = Just x
  mappend Nothing  (Just y) = Just y
  mappend Nothing  Nothing  = Nothing

  mempty = Nothing

Both is a newtype wrapper around Maybe providing this instance:

instance Monoid a => Monoid (Both a) where
  mappend (Just x) (Just y) = Just $ x <> y
  mappend _ _ = Nothing

  mempty = Just mempty