Add definitions for stimes (#340)

Also remove unused `LambdaCase` extension.

Resolves part of #307.

Data/HashMap/Internal.hs

@@ -142,9 +142,7 @@ module Data.HashMap.Internal
     , adjust#
     ) where
 
-#if !MIN_VERSION_base(4,11,0)
-import Data.Semigroup (Semigroup((<>)))
-#endif
+import Data.Semigroup (Semigroup(..), stimesIdempotentMonoid)
 import Control.DeepSeq (NFData(rnf))
 import Control.Monad.ST (ST, runST)
 import Data.Bits ((.&.), (.|.), complement, popCount, unsafeShiftL, unsafeShiftR)
@@ -296,6 +294,8 @@ instance Bifoldable HashMap where
 instance (Eq k, Hashable k) => Semigroup (HashMap k v) where
   (<>) = union
   {-# INLINE (<>) #-}
+  stimes = stimesIdempotentMonoid
+  {-# INLINE stimes #-}
 
 -- | 'mempty' = 'empty'
 --

Data/HashMap/Internal/Strict.hs

@@ -1,5 +1,4 @@
 {-# LANGUAGE BangPatterns, CPP, PatternGuards, MagicHash, UnboxedTuples #-}
-{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE Trustworthy #-}
 {-# OPTIONS_HADDOCK not-home #-}
 

Data/HashSet/Internal.hs

@@ -97,9 +97,7 @@ import Data.HashMap.Internal
   ( HashMap, foldMapWithKey, foldlWithKey, foldrWithKey
   , equalKeys, equalKeys1)
 import Data.Hashable (Hashable(hashWithSalt))
-#if !MIN_VERSION_base(4,11,0)
-import Data.Semigroup (Semigroup(..))
-#endif
+import Data.Semigroup (Semigroup(..), stimesIdempotentMonoid)
 import GHC.Exts (build)
 import qualified GHC.Exts as Exts
 import Prelude hiding (filter, foldr, foldl, map, null)
@@ -200,6 +198,8 @@ instance Foldable.Foldable HashSet where
 instance (Hashable a, Eq a) => Semigroup (HashSet a) where
     (<>) = union
     {-# INLINE (<>) #-}
+    stimes = stimesIdempotentMonoid
+    {-# INLINE stimes #-}
 
 -- | 'mempty' = 'empty'
 --