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Diffstat (limited to 'libraries/base/GHC/ST.hs')
| -rw-r--r-- | libraries/base/GHC/ST.hs | 5 |
1 files changed, 5 insertions, 0 deletions
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 |