Simplify TokenMap.maximumQuantity.

lib/primitive/lib/Cardano/Wallet/Primitive/Types/TokenMap.hs

@@ -156,7 +156,6 @@ import qualified Data.Aeson as Aeson
 import qualified Data.Foldable as F
 import qualified Data.List as L
 import qualified Data.List.NonEmpty as NE
-import qualified Data.Map.Strict as Map
 import qualified Data.Monoid.Null as MonoidNull
 import qualified Data.MonoidMap as MonoidMap
 import qualified Data.Set as Set
@@ -662,20 +661,7 @@ removeQuantity m asset = setQuantity m asset TokenQuantity.zero
 -- | Get the largest quantity from this map.
 --
 maximumQuantity :: TokenMap -> TokenQuantity
-maximumQuantity
-    = Map.foldl' (\a -> Map.foldr findMaximum a . MonoidMap.toMap) zero
-    . MonoidMap.toMap
-    . unTokenMap
-  where
-    zero :: TokenQuantity
-    zero = TokenQuantity 0
-
-    findMaximum :: TokenQuantity -> TokenQuantity -> TokenQuantity
-    findMaximum challenger champion
-        | challenger > champion =
-            challenger
-        | otherwise =
-            champion
+maximumQuantity = F.foldl' (F.foldr max) mempty . unTokenMap
 
 --------------------------------------------------------------------------------
 -- Partitioning

lib/primitive/test/spec/Cardano/Wallet/Primitive/Types/TokenMapSpec.hs

@@ -264,6 +264,8 @@ spec =
             property prop_adjustQuantity_hasQuantity
         it "prop_maximumQuantity_all" $
             property prop_maximumQuantity_all
+        it "prop_maximumQuantity_mempty" $
+            property prop_maximumQuantity_mempty
 
     parallel $ describe "Queries" $ do
 
@@ -705,6 +707,9 @@ prop_maximumQuantity_all b =
   where
     maxQ = TokenMap.maximumQuantity b
 
+prop_maximumQuantity_mempty :: Property
+prop_maximumQuantity_mempty = TokenMap.maximumQuantity mempty === mempty
+
 --------------------------------------------------------------------------------
 -- Queries
 --------------------------------------------------------------------------------