Cleanup: Remove type class Dom

* it was only instantiated for `UTxO` * after recent commits, it is only occurring in testing code
cardano-foundation · Feb 25, 2022 · caf3ac8 · caf3ac8
1 parent fb89813
commit caf3ac8
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diff --git a/docs/user-guide/faq.md b/docs/user-guide/faq.md
@@ -51,21 +51,15 @@ Wallet Backend specifications, the notation is inspired from the [Z notation](ht
 <details>
   <summary>What is <code>dom</code> from <strong>Lemma 2.1</strong></summary>
 
-  There are multiple occurrences in the spec of expressions like: `(dom u ∩ ins) ◃ u`. The meaning of `dom u` isn't quite clearly defined anywhere but refers to the set of keys from the mapping defined by `u: txin ↦ txout`. Hence,
-`dom u` refers to all `txin` available in `u`.
+  There are multiple occurrences in the spec of expressions like: `(dom u ∩ ins) ◃ u`. The meaning of `dom u` isn't quite clearly defined anywhere but refers to the set of keys from the mapping defined by `u: txin ↦ txout`. Hence, `dom u` refers to all `txin` available in `u`.
 
   In Haskell, this translates to:
 
   ```hs
-  class Dom a where
-    type DomElem a :: *
-    dom :: a -> Set (DomElem a)
-
   newtype UTxO = UTxO (Map TxIn TxOut)
 
-  instance Dom UTxO where
-    type DomElem UTxO = TxIn
-    dom (UTxO utxo)   = Set.fromList $ Map.keys utxo
+  dom :: UTxO -> Set TxIn
+  dom (UTxO utxo) = Set.fromList $ Map.keys utxo
   ```
 </details>
 

diff --git a/lib/core/src/Cardano/Wallet/Primitive/Types/UTxO.hs b/lib/core/src/Cardano/Wallet/Primitive/Types/UTxO.hs
@@ -18,8 +18,8 @@ module Cardano.Wallet.Primitive.Types.UTxO
     (
     -- * UTxO
       UTxO (..)
-    , Dom (..)
 
+    , dom
     , null
     , size
     , balance
@@ -73,8 +73,6 @@ import Data.Functor.Identity
     ( runIdentity )
 import Data.Generics.Internal.VL.Lens
     ( view )
-import Data.Kind
-    ( Type )
 import Data.List.NonEmpty
     ( NonEmpty (..) )
 import Data.Map.Strict
@@ -106,17 +104,6 @@ newtype UTxO = UTxO { unUTxO :: Map TxIn TxOut }
 
 instance NFData UTxO
 
--- | Allows us to define the "domain" of any type — @UTxO@ in particular — and
--- use 'dom' to refer to the /inputs/ of an /utxo/.
---
-class Dom a where
-    type DomElem a :: Type
-    dom :: a -> Set (DomElem a)
-
-instance Dom UTxO where
-    type DomElem UTxO = TxIn
-    dom (UTxO utxo) = Map.keysSet utxo
-
 instance Buildable UTxO where
     build (UTxO utxo) =
         blockListF' "-" utxoF (Map.toList utxo)
@@ -129,6 +116,10 @@ instance Buildable UTxO where
             ]
         buildMap = blockMapF . fmap (first $ id @String)
 
+-- | Domain of a 'UTxO' = the set of /inputs/ of the /utxo/.
+dom :: UTxO -> Set TxIn
+dom (UTxO utxo) = Map.keysSet utxo
+
 -- | Compute the balance of a UTxO
 balance :: UTxO -> TokenBundle
 balance =

diff --git a/lib/core/test/unit/Cardano/Wallet/Primitive/ModelSpec.hs b/lib/core/test/unit/Cardano/Wallet/Primitive/ModelSpec.hs
@@ -88,7 +88,7 @@ import Cardano.Wallet.Primitive.Types.Tx
 import Cardano.Wallet.Primitive.Types.Tx.Gen
     ( genTx, genTxIn, genTxOut, shrinkTx, shrinkTxIn, shrinkTxOut )
 import Cardano.Wallet.Primitive.Types.UTxO
-    ( Dom (..), UTxO (..), balance, excluding, filterByAddress, restrictedTo )
+    ( UTxO (..), balance, dom, excluding, filterByAddress, restrictedTo )
 import Cardano.Wallet.Primitive.Types.UTxO.Gen
     ( genUTxO, shrinkUTxO )
 import Cardano.Wallet.Util

diff --git a/lib/core/test/unit/Cardano/Wallet/Primitive/TypesSpec.hs b/lib/core/test/unit/Cardano/Wallet/Primitive/TypesSpec.hs
@@ -111,12 +111,12 @@ import Cardano.Wallet.Primitive.Types.Tx.Gen
     ( genTx, shrinkTx )
 import Cardano.Wallet.Primitive.Types.UTxO
     ( BoundType
-    , Dom (..)
     , HistogramBar (..)
     , UTxO (..)
     , UTxOStatistics (..)
     , balance
     , computeUtxoStatistics
+    , dom
     , excluding
     , isSubsetOf
     , log10