Revise definitions of stimes. (#187)

src/examples/Examples/RecoveredMap.hs

@@ -15,12 +15,16 @@ import Prelude hiding
 
 import Control.DeepSeq
     ( NFData )
+import Data.Coerce
+    ( coerce )
 import Data.Maybe
     ( mapMaybe )
 import Data.Monoid
     ( First (..) )
 import Data.MonoidMap
     ( MonoidMap )
+import Data.Semigroup
+    ( Semigroup (stimes), stimesIdempotentMonoid )
 import Data.Set
     ( Set )
 
@@ -29,7 +33,11 @@ import qualified Data.MonoidMap as MonoidMap
 newtype Map k v = Map
     --  'First' is used to mimic the left-biased nature of 'Data.Map':
     {unMap :: MonoidMap k (First v)}
-    deriving newtype (Eq, NFData, Semigroup, Monoid)
+    deriving newtype (Eq, NFData, Monoid)
+
+instance Ord k => Semigroup (Map k v) where
+    (<>) = coerce @(MonoidMap k (First v) -> _ -> _) (<>)
+    stimes = stimesIdempotentMonoid
 
 instance (Show k, Show v) => Show (Map k v) where
     show = ("fromList " <>) . show . toList

src/internal/Data/MonoidMap/Internal.hs

@@ -244,6 +244,8 @@ instance (Ord k, MonoidNull v) =>
     Semigroup (MonoidMap k v)
   where
     (<>) = append
+    stimes 0 = const mempty
+    stimes 1 = id
     stimes n = map (stimes n)
 
 instance (Ord k, MonoidNull v, Commutative v) =>

src/test/Examples/RecoveredMapSpec.hs

@@ -21,6 +21,8 @@ import Data.Monoid
     ( Sum (..) )
 import Data.Proxy
     ( Proxy (..) )
+import Data.Semigroup
+    ( Semigroup (stimes) )
 import Data.Set
     ( Set )
 import Data.Text
@@ -36,6 +38,7 @@ import Test.QuickCheck
     , CoArbitrary
     , Fun
     , Function
+    , NonNegative (..)
     , Property
     , Testable
     , applyFun
@@ -148,6 +151,11 @@ specFor keyType valueType = do
                 prop_append_toList
                     @k @v & property
 
+        describe "Times" $ do
+            it "prop_stimes_toList" $
+                prop_stimes_toList
+                    @k @v & property
+
         describe "Delete" $ do
             it "prop_delete_lookup" $
                 prop_delete_lookup
@@ -301,6 +309,29 @@ prop_append_toList kvs1 kvs2 =
     ks1 = Set.fromList (fst <$> kvs1)
     ks2 = Set.fromList (fst <$> kvs2)
 
+--------------------------------------------------------------------------------
+-- Times
+--------------------------------------------------------------------------------
+
+prop_stimes_toList
+    :: forall k v. (Ord k, Show k, Eq v, Show v)
+    => [(k, v)]
+    -> NonNegative Int
+    -> Property
+prop_stimes_toList kvs (NonNegative n) =
+    (===)
+        (RMap.toList (stimes n (RMap.fromList kvs)))
+        (OMap.toList (stimes n (OMap.fromList kvs)))
+    & cover 1
+        (n == 0)
+        "n == 0"
+    & cover 1
+        (n == 1)
+        "n == 1"
+    & cover 10
+        (n >= 2)
+        "n >= 2"
+
 --------------------------------------------------------------------------------
 -- Delete
 --------------------------------------------------------------------------------