move 'addCoin' and 'subtractCoin' to the Primitive/Coin module

They better fit there than in the RoundRobin module.
cardano-foundation · Jan 20, 2021 · c1d62da · c1d62da
1 parent 0dde4a5
commit c1d62da
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Showing 3 changed files with 29 additions and 14 deletions.
diff --git a/lib/core/src/Cardano/Wallet/Primitive/CoinSelection/MA/RoundRobin.hs b/lib/core/src/Cardano/Wallet/Primitive/CoinSelection/MA/RoundRobin.hs
@@ -60,8 +60,6 @@ module Cardano.Wallet.Primitive.CoinSelection.MA.RoundRobin
     -- * Utility functions
     , distance
     , mapMaybe
-    , subtractCoin
-    , addCoin
     ) where
 
 import Prelude
@@ -71,7 +69,7 @@ import Algebra.PartialOrd
 import Cardano.Numeric.Util
     ( padCoalesce, partitionNatural )
 import Cardano.Wallet.Primitive.Types.Coin
-    ( Coin (..) )
+    ( Coin (..), subtractCoin )
 import Cardano.Wallet.Primitive.Types.TokenBundle
     ( TokenBundle (..) )
 import Cardano.Wallet.Primitive.Types.TokenMap
@@ -839,11 +837,3 @@ mapMaybe predicate (x :| xs) = go (x:xs)
         case predicate a of
             Just b  -> b : go as
             Nothing -> go as
-
-subtractCoin :: Coin -> Coin -> Maybe Coin
-subtractCoin (Coin a) (Coin b)
-    | a >= b    = Just $ Coin (a - b)
-    | otherwise = Nothing
-
-addCoin :: Coin -> Coin -> Coin
-addCoin (Coin a) (Coin b) = Coin (a + b)
diff --git a/lib/core/src/Cardano/Wallet/Primitive/Types/Coin.hs b/lib/core/src/Cardano/Wallet/Primitive/Types/Coin.hs
@@ -15,9 +15,12 @@ module Cardano.Wallet.Primitive.Types.Coin
     -- * Type
       Coin (..)
 
+    -- * Operations
+    , addCoin
+    , subtractCoin
+
     -- * Checks
     , isValidCoin
-
     ) where
 
 import Prelude
@@ -72,5 +75,28 @@ instance Bounded Coin where
 instance Buildable Coin where
     build = build . unCoin
 
+--------------------------------------------------------------------------------
+-- Operations
+--------------------------------------------------------------------------------
+
+-- | Subtract a coin quantity to another, returning nothing if the second
+-- argument is strictly bigger than the first.
+subtractCoin :: Coin -> Coin -> Maybe Coin
+subtractCoin (Coin a) (Coin b)
+    | a >= b    = Just $ Coin (a - b)
+    | otherwise = Nothing
+
+-- NOTE: It is generally safe to add coins and stay in the same domain because
+-- the max supply is known (45B), which largely fits within a `Word64`. So in
+-- the vaste majority of usages of this function within cardano-wallet, it is a
+-- safe operation.
+--
+addCoin :: Coin -> Coin -> Coin
+addCoin (Coin a) (Coin b) = Coin (a + b)
+
+--------------------------------------------------------------------------------
+-- Checks
+--------------------------------------------------------------------------------
+
 isValidCoin :: Coin -> Bool
 isValidCoin c = c >= minBound && c <= maxBound
diff --git a/lib/core/test/unit/Cardano/Wallet/Primitive/CoinSelection/MA/RoundRobinSpec.hs b/lib/core/test/unit/Cardano/Wallet/Primitive/CoinSelection/MA/RoundRobinSpec.hs
@@ -28,7 +28,6 @@ import Cardano.Wallet.Primitive.CoinSelection.MA.RoundRobin
     , SelectionResult (..)
     , SelectionSkeleton (..)
     , SelectionState (..)
-    , addCoin
     , fullBalance
     , groupByKey
     , makeChange
@@ -44,7 +43,7 @@ import Cardano.Wallet.Primitive.CoinSelection.MA.RoundRobin
     , ungroupByKey
     )
 import Cardano.Wallet.Primitive.Types.Coin
-    ( Coin (..) )
+    ( Coin (..), addCoin )
 import Cardano.Wallet.Primitive.Types.Coin.Gen
     ( genCoinSmall, genCoinSmallPositive, shrinkCoinSmallPositive )
 import Cardano.Wallet.Primitive.Types.Hash