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| -rw-r--r-- | libraries/base/Data/Monoid.hs | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/libraries/base/Data/Monoid.hs b/libraries/base/Data/Monoid.hs index b6d09c1f2d..d11eda8a00 100644 --- a/libraries/base/Data/Monoid.hs +++ b/libraries/base/Data/Monoid.hs @@ -88,6 +88,16 @@ import Data.Semigroup.Internal -- -- >>> getFirst (First (Just "hello") <> First Nothing <> First (Just "world")) -- Just "hello" +-- +-- Use of this type is discouraged. Note the following equivalence: +-- +-- > Data.Monoid.First x === Maybe (Data.Semigroup.First x) +-- +-- In additional to being equivalent in the structural sense, the two +-- also have 'Monoid' instances that behave the same. This type will +-- be marked deprecated in GHC 8.8. It will be removed in GHC 8.10. +-- Users are advised to use the variant from "Data.Semigroup" and wrap +-- it in 'Maybe'. newtype First a = First { getFirst :: Maybe a } deriving ( Eq -- ^ @since 2.01 , Ord -- ^ @since 2.01 |