Add Monoid instance for TokenBundle.

cardano-foundation · Jan 11, 2021 · 1484b3a · 1484b3a
1 parent 7bab9c2
commit 1484b3a
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Showing 2 changed files with 11 additions and 1 deletion.
diff --git a/lib/core/src/Cardano/Wallet/Primitive/Types/TokenBundle.hs b/lib/core/src/Cardano/Wallet/Primitive/Types/TokenBundle.hs
@@ -126,6 +126,9 @@ instance NFData TokenBundle
 instance Semigroup TokenBundle where
     (<>) = add
 
+instance Monoid TokenBundle where
+    mempty = empty
+
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 -- Text serialization
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@@ -155,6 +158,11 @@ buildMap = blockMapF . fmap (first $ id @String)
 -- Construction
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+-- | The empty token bundle.
+--
+empty :: TokenBundle
+empty = TokenBundle (Coin 0) mempty
+
 -- | Creates a token bundle from a coin and a flat list of token quantities.
 --
 -- If a token name appears more than once in the list under the same policy,

diff --git a/lib/core/test/unit/Cardano/Wallet/Primitive/Types/TokenBundleSpec.hs b/lib/core/test/unit/Cardano/Wallet/Primitive/Types/TokenBundleSpec.hs
@@ -19,7 +19,7 @@ import Test.Hspec.Core.QuickCheck
 import Test.QuickCheck
     ( Arbitrary (..) )
 import Test.QuickCheck.Classes
-    ( eqLaws, semigroupLaws )
+    ( eqLaws, monoidLaws, semigroupLaws, semigroupMonoidLaws )
 import Test.Utils.Laws
     ( testLawsMany )
 import Test.Utils.Laws.PartialOrd
@@ -33,8 +33,10 @@ spec =
     describe "Class instances obey laws" $ do
         testLawsMany @TokenBundle
             [ eqLaws
+            , monoidLaws
             , partialOrdLaws
             , semigroupLaws
+            , semigroupMonoidLaws
             ]
 
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