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| author | Ben Gamari <ben@smart-cactus.org> | 2017-08-14 20:58:16 -0400 |
|---|---|---|
| committer | Ben Gamari <ben@smart-cactus.org> | 2017-08-14 21:32:17 -0400 |
| commit | 441c52de0621ac68a2248cf691b4de31fba48a34 (patch) | |
| tree | be97549925f8ab6d8670423ad89992aaf3021dc9 /libraries | |
| parent | a520adcce27908c799b64214618cf9b33572dc37 (diff) | |
| download | haskell-441c52de0621ac68a2248cf691b4de31fba48a34.tar.gz | |
Add Semigroup/Monoid instances to ST monad
Fixes #14107.
Signed-off-by: Philipp Middendorf <middendorf@plapadoo.de>
Reviewers: austin, hvr, bgamari, RyanGlScott
Reviewed By: bgamari
Subscribers: RyanGlScott, rwbarton, thomie
GHC Trac Issues: #14107
Differential Revision: https://phabricator.haskell.org/D3845
Diffstat (limited to 'libraries')
| -rw-r--r-- | libraries/base/Data/Semigroup.hs | 5 | ||||
| -rw-r--r-- | libraries/base/GHC/ST.hs | 5 | ||||
| -rw-r--r-- | libraries/base/changelog.md | 2 |
3 files changed, 12 insertions, 0 deletions
diff --git a/libraries/base/Data/Semigroup.hs b/libraries/base/Data/Semigroup.hs index fae207ef97..8631b117be 100644 --- a/libraries/base/Data/Semigroup.hs +++ b/libraries/base/Data/Semigroup.hs @@ -72,6 +72,7 @@ import Prelude hiding (foldr1) import Control.Applicative import Control.Monad import Control.Monad.Fix +import Control.Monad.ST(ST) import Data.Bifoldable import Data.Bifunctor import Data.Bitraversable @@ -725,6 +726,10 @@ instance Semigroup (Proxy s) where instance Semigroup a => Semigroup (IO a) where (<>) = liftA2 (<>) +-- | @since 4.11.0.0 +instance Semigroup a => Semigroup (ST s a) where + (<>) = liftA2 (<>) + #if !defined(mingw32_HOST_OS) -- | @since 4.10.0.0 instance Semigroup Event where diff --git a/libraries/base/GHC/ST.hs b/libraries/base/GHC/ST.hs index 4e00c0e85f..a245b9fc50 100644 --- a/libraries/base/GHC/ST.hs +++ b/libraries/base/GHC/ST.hs @@ -77,6 +77,11 @@ instance Monad (ST s) where case (k r) of { ST k2 -> (k2 new_s) }}) +-- | @since 4.11.0.0 +instance Monoid a => Monoid (ST s a) where + mempty = pure mempty + mappend = liftA2 mappend + data STret s a = STret (State# s) a -- liftST is useful when we want a lifted result from an ST computation. See diff --git a/libraries/base/changelog.md b/libraries/base/changelog.md index 708676fe65..ab304a317f 100644 --- a/libraries/base/changelog.md +++ b/libraries/base/changelog.md @@ -14,6 +14,8 @@ * Remove the deprecated `Typeable{1..7}` type synonyms (#14047) + * Add instances `Semigroup` and `Monoid` for `Control.Monad.ST` (#14107). + ## 4.10.0.0 *April 2017* * Bundled with GHC *TBA* |