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| author | Andrew Martin <andrew.thaddeus@gmail.com> | 2018-04-25 21:01:25 -0400 |
|---|---|---|
| committer | Ben Gamari <ben@smart-cactus.org> | 2018-05-03 12:00:56 -0400 |
| commit | cf35ab9ac7e0f33e39af6af16ecf850e24c2cb79 (patch) | |
| tree | df36c439c7ab30d1c7c1cc343b6748611afe3e32 /libraries/base | |
| parent | 90589a942b770b9c373a73b6c1d17487fdcf4d9b (diff) | |
| download | haskell-cf35ab9ac7e0f33e39af6af16ecf850e24c2cb79.tar.gz | |
minor improvement to wording of warning against First. Add warning against Last
Diffstat (limited to 'libraries/base')
| -rw-r--r-- | libraries/base/Data/Monoid.hs | 12 |
1 files changed, 11 insertions, 1 deletions
diff --git a/libraries/base/Data/Monoid.hs b/libraries/base/Data/Monoid.hs index d11eda8a00..aa3000ad3b 100644 --- a/libraries/base/Data/Monoid.hs +++ b/libraries/base/Data/Monoid.hs @@ -95,7 +95,7 @@ import Data.Semigroup.Internal -- -- 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. +-- be marked deprecated in GHC 8.8, and 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 } @@ -127,6 +127,16 @@ instance Monoid (First a) where -- -- >>> getLast (Last (Just "hello") <> Last Nothing <> Last (Just "world")) -- Just "world" +-- +-- Use of this type is discouraged. Note the following equivalence: +-- +-- > Data.Monoid.Last x === Maybe (Data.Semigroup.Last 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, and removed in GHC 8.10. +-- Users are advised to use the variant from "Data.Semigroup" and wrap +-- it in 'Maybe'. newtype Last a = Last { getLast :: Maybe a } deriving ( Eq -- ^ @since 2.01 , Ord -- ^ @since 2.01 |