[commit: ghc] master: minor improvement to wording of warning against First. Add warning against Last (cf35ab9)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/cf35ab9ac7e0f33e39af6af16ecf850e24c2cb79/ghc

>---------------------------------------------------------------

commit cf35ab9ac7e0f33e39af6af16ecf850e24c2cb79
Author: Andrew Martin <andrew.thaddeus at gmail.com>
Date:   Wed Apr 25 21:01:25 2018 -0400

    minor improvement to wording of warning against First. Add warning against Last


>---------------------------------------------------------------

cf35ab9ac7e0f33e39af6af16ecf850e24c2cb79
 libraries/base/Data/Monoid.hs | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/libraries/base/Data/Monoid.hs b/libraries/base/Data/Monoid.hs
index d11eda8..aa3000a 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