Add Default instances for some Shelley states.

Shelley states (most of which can be found in `module
Shelley.Spec.Ledger.LedgerState`) have now a `Default` instance, which means
that they have a default value. This default value is what it was previously
know as "empty" state. Furthermore, the STS class provides a `default`
definition for initial rules of STS whose state has a `Default` instance:

```
default initialRules :: Default (State a) => [InitialRule a]
initialRules = [pure def]
```

semantics/executable-spec/small-steps.cabal

@@ -48,6 +48,7 @@ library
                      , cborg
                      , containers
                      , cryptonite
+                     , data-default-class
                      , deepseq
                      , free
                      , mtl

semantics/executable-spec/src/Control/State/Transition/Extended.hs

@@ -2,6 +2,7 @@
 {-# LANGUAGE BangPatterns #-}
 {-# LANGUAGE CPP #-}
 {-# LANGUAGE DataKinds #-}
+{-# LANGUAGE DefaultSignatures #-}
 {-# LANGUAGE DeriveDataTypeable #-}
 {-# LANGUAGE DeriveFunctor #-}
 {-# LANGUAGE FlexibleContexts #-}
@@ -63,6 +64,7 @@ import Control.Monad.Trans.Class (lift)
 import Control.Monad.Trans.State.Strict (modify, runStateT)
 import qualified Control.Monad.Trans.State.Strict as MonadState
 import Data.Data (Data, Typeable)
+import Data.Default.Class (Default, def)
 import Data.Foldable (find, traverse_)
 import Data.Functor ((<&>))
 import Data.Kind (Type)
@@ -180,6 +182,8 @@ class
 
   -- | Rules governing transition under this system.
   initialRules :: [InitialRule a]
+  default initialRules :: Default (State a) => [InitialRule a]
+  initialRules = [pure def]
 
   transitionRules :: [TransitionRule a]
 

shelley-ma/shelley-ma-test/cardano-ledger-shelley-ma-test.cabal

@@ -104,6 +104,7 @@ test-suite cardano-ledger-shelley-ma-test
       "-with-rtsopts=-K4m -M250m"
     build-depends:
       cardano-ledger-shelley-ma,
+      data-default-class,
       shelley-spec-ledger-test,
       cardano-ledger-shelley-ma-test,
       base >=4.9 && <4.15,

shelley-ma/shelley-ma-test/test/Test/Cardano/Ledger/Allegra/ScriptTranslation.hs

@@ -18,7 +18,7 @@ import Shelley.Spec.Ledger.UTxO (txid)
 import Test.Tasty (TestTree)
 import Test.Tasty.HUnit (testCase)
 import Test.Shelley.Spec.Ledger.Utils (runShelleyBase, applySTSTest)
-import Shelley.Spec.Ledger.LedgerState (emptyUTxOState, emptyDPState)
+import Shelley.Spec.Ledger.LedgerState ()
 import Control.State.Transition.Extended (TRC (..))
 import Control.Monad.Except (runExcept)
 import Shelley.Spec.Ledger.Tx (hashScript, scriptWits)
@@ -29,6 +29,7 @@ import Test.Cardano.Ledger.EraBuffet
     ShelleyEra,
     StandardCrypto,
   )
+import Data.Default.Class (def)
 
 type Allegra = AllegraEra StandardCrypto
 
@@ -73,7 +74,7 @@ testScriptPostTranslation = testCase
           (S.TxIn bootstrapTxId 0)
           (S.TxOut addr (Val.inject (S.Coin 1)))
     env = S.LedgerEnv (SlotNo 0) 0 emptyPParams (S.AccountState (S.Coin 0) (S.Coin 0))
-    utxoStShelley = emptyUTxOState {S._utxo = utxo}
+    utxoStShelley = def {S._utxo = utxo}
     utxoStAllegra = fromRight . runExcept $ translateEra @Allegra () utxoStShelley
     txb =
       S.TxBody
@@ -90,7 +91,7 @@ testScriptPostTranslation = testCase
     txa = fromRight . runExcept $ translateEra @Allegra () txs
     result = runShelleyBase $
       applySTSTest @(S.LEDGER Allegra)
-        (TRC (env, (utxoStAllegra, emptyDPState), txa))
+        (TRC (env, (utxoStAllegra, def), txa))
     in
     case result of
       Left e -> error $ show e

shelley-ma/shelley-ma-test/test/Test/Cardano/Ledger/Mary/Examples.hs

@@ -16,15 +16,14 @@ import GHC.Records
 import Shelley.Spec.Ledger.API (LEDGER, LedgerEnv (..))
 import Shelley.Spec.Ledger.LedgerState
   ( DPState (..),
-    UTxOState (..),
-    emptyDPState,
-    emptyUTxOState,
+    UTxOState (..)
   )
 import Shelley.Spec.Ledger.Tx (Tx (..))
 import Shelley.Spec.Ledger.UTxO (UTxO)
 import Test.Cardano.Ledger.EraBuffet (TestCrypto)
 import Test.Shelley.Spec.Ledger.Utils (applySTSTest, runShelleyBase)
 import Test.Tasty.HUnit (Assertion, (@?=))
+import Data.Default.Class (def)
 
 type MaryTest = MaryEra TestCrypto
 
@@ -42,10 +41,10 @@ testMaryNoDelegLEDGER ::
   Assertion
 testMaryNoDelegLEDGER utxo tx env (Right expectedUTxO) = do
   checkTrace @(LEDGER MaryTest) runShelleyBase env $
-    pure (emptyUTxOState {_utxo = utxo}, emptyDPState) .- tx .-> expectedSt'
+    pure (def {_utxo = utxo}, def) .- tx .-> expectedSt'
   where
     txFee = getField @"txfee" (_body tx)
-    expectedSt' = (emptyUTxOState {_utxo = expectedUTxO, _fees = txFee}, emptyDPState)
+    expectedSt' = (def {_utxo = expectedUTxO, _fees = txFee}, def)
 testMaryNoDelegLEDGER utxo tx env predicateFailure@(Left _) = do
-  let st = runShelleyBase $ applySTSTest @(LEDGER MaryTest) (TRC (env, (emptyUTxOState {_utxo = utxo}, emptyDPState), tx))
+  let st = runShelleyBase $ applySTSTest @(LEDGER MaryTest) (TRC (env, (def {_utxo = utxo}, def), tx))
   (ignoreAllButUTxO st) @?= predicateFailure

shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/API/ByronTranslation.hs

@@ -22,6 +22,7 @@ import qualified Cardano.Ledger.Crypto as CC
 import Cardano.Ledger.Shelley (ShelleyEra)
 import Cardano.Ledger.Val ((<->))
 import qualified Data.ByteString.Short as SBS
+import Data.Default.Class (def)
 import qualified Data.Map.Strict as Map
 import Data.Maybe (fromMaybe)
 import GHC.Stack (HasCallStack)
@@ -30,8 +31,6 @@ import Shelley.Spec.Ledger.API.Types
 import Shelley.Spec.Ledger.Coin (CompactForm (CompactCoin))
 import Shelley.Spec.Ledger.CompactAddr (CompactAddr (UnsafeCompactAddr))
 import Shelley.Spec.Ledger.EpochBoundary
-import Shelley.Spec.Ledger.LedgerState
-import Shelley.Spec.Ledger.Rewards
 import Shelley.Spec.Ledger.STS.Chain (pparamsToChainChecksData)
 import Shelley.Spec.Ledger.Slot
 
@@ -130,7 +129,7 @@ translateToShelleyLedgerState genesisShelley epochNo cvs =
           esLState = ledgerState,
           esPrevPp = pparams,
           esPp = pparams,
-          esNonMyopic = emptyNonMyopic
+          esNonMyopic = def
         }
 
     utxoByron :: Byron.UTxO
@@ -147,12 +146,12 @@ translateToShelleyLedgerState genesisShelley epochNo cvs =
               { _utxo = utxoShelley,
                 _deposited = Coin 0,
                 _fees = Coin 0,
-                _ppups = emptyPPUPState
+                _ppups = def
               },
           _delegationState =
             DPState
-              { _dstate = emptyDState {_genDelegs = genDelegs},
-                _pstate = emptyPState
+              { _dstate = def {_genDelegs = genDelegs},
+                _pstate = def
               }
         }
 

shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/EpochBoundary.hs

@@ -41,6 +41,7 @@ import qualified Cardano.Ledger.Val as Val
 import Control.DeepSeq (NFData)
 import Control.SetAlgebra (dom, eval, setSingleton, (▷), (◁))
 import Data.Aeson
+import Data.Default.Class (Default, def)
 import Data.Map.Strict (Map)
 import qualified Data.Map.Strict as Map
 import Data.Ratio ((%))
@@ -230,6 +231,9 @@ instance
       f <- fromCBOR
       pure $ SnapShots mark set go f
 
+instance Default (SnapShots crypto) where
+  def = emptySnapShots
+
 emptySnapShot :: SnapShot crypto
 emptySnapShot = SnapShot (Stake Map.empty) Map.empty Map.empty
 

shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/LedgerState.hs

@@ -42,24 +42,12 @@ module Shelley.Spec.Ledger.LedgerState
     RewardUpdate (..),
     UTxOState (..),
     depositPoolChange,
-    emptyAccount,
-    emptyDPState,
-    emptyDState,
-    emptyEpochState,
-    emptyInstantaneousRewards,
-    emptyLedgerState,
-    emptyPPUPState,
-    emptyPState,
     emptyRewardUpdate,
-    emptyUTxOState,
     pvCanFollow,
     reapRewards,
     totalInstantaneousReservesRewards,
     updatePpup,
 
-    -- * state transitions
-    emptyDelegation,
-
     -- * Genesis State
     genesisState,
 
@@ -129,6 +117,7 @@ import Control.SetAlgebra (Bimap, biMapEmpty, dom, eval, forwards, range, (∈),
 import qualified Data.ByteString.Lazy as BSL (length)
 import Data.Coerce (coerce)
 import Data.Constraint (Constraint)
+import Data.Default.Class (Default, def)
 import Data.Foldable (fold, toList)
 import Data.Group (invert)
 import Data.Kind (Type)
@@ -181,7 +170,6 @@ import Shelley.Spec.Ledger.EpochBoundary
     SnapShots (..),
     Stake (..),
     aggregateUtxoCoinByCredential,
-    emptySnapShots,
   )
 import Shelley.Spec.Ledger.Hashing (hashAnnotated)
 import Shelley.Spec.Ledger.Keys
@@ -202,7 +190,6 @@ import Shelley.Spec.Ledger.PParams
     ProtVer (..),
     Update (..),
     emptyPPPUpdates,
-    emptyPParams,
   )
 import Shelley.Spec.Ledger.RewardProvenance (Desirability (..), RewardProvenance (..))
 import Shelley.Spec.Ledger.Rewards
@@ -211,7 +198,6 @@ import Shelley.Spec.Ledger.Rewards
     PerformanceEstimate (..),
     applyDecay,
     desirability,
-    emptyNonMyopic,
     percentile',
     reward,
   )
@@ -452,7 +438,8 @@ instance
       pure $ RewardUpdate dt (invert dr) rw (invert df) nm
 
 emptyRewardUpdate :: RewardUpdate crypto
-emptyRewardUpdate = RewardUpdate (DeltaCoin 0) (DeltaCoin 0) Map.empty (DeltaCoin 0) emptyNonMyopic
+emptyRewardUpdate =
+  RewardUpdate (DeltaCoin 0) (DeltaCoin 0) Map.empty (DeltaCoin 0) def
 
 data AccountState = AccountState
   { _treasury :: !Coin,
@@ -521,49 +508,6 @@ instance
       n <- fromCBOR
       pure $ EpochState a s l r p n
 
-emptyPPUPState :: PPUPState era
-emptyPPUPState = PPUPState emptyPPPUpdates emptyPPPUpdates
-
-emptyUTxOState :: UTxOState era
-emptyUTxOState = UTxOState (UTxO Map.empty) (Coin 0) (Coin 0) emptyPPUPState
-
-emptyEpochState :: EpochState era
-emptyEpochState =
-  EpochState emptyAccount emptySnapShots emptyLedgerState emptyPParams emptyPParams emptyNonMyopic
-
-emptyLedgerState :: LedgerState era
-emptyLedgerState =
-  LedgerState
-    emptyUTxOState
-    emptyDelegation
-
-emptyAccount :: AccountState
-emptyAccount = AccountState (Coin 0) (Coin 0)
-
-emptyDelegation :: DPState crypto
-emptyDelegation =
-  DPState emptyDState emptyPState
-
-emptyInstantaneousRewards :: InstantaneousRewards crypto
-emptyInstantaneousRewards = InstantaneousRewards Map.empty Map.empty
-
-emptyDState :: DState crypto
-emptyDState =
-  DState
-    Map.empty
-    Map.empty
-    biMapEmpty
-    Map.empty
-    (GenDelegs Map.empty)
-    emptyInstantaneousRewards
-
-emptyPState :: PState crypto
-emptyPState =
-  PState Map.empty Map.empty Map.empty
-
-emptyDPState :: DPState crypto
-emptyDPState = DPState emptyDState emptyPState
-
 data PPUPState era = PPUPState
   { proposals :: !(ProposedPPUpdates era),
     futureProposals :: !(ProposedPPUpdates era)
@@ -762,11 +706,11 @@ genesisState genDelegs0 utxo0 =
         utxo0
         (Coin 0)
         (Coin 0)
-        emptyPPUPState
+        def
     )
-    (DPState dState emptyPState)
+    (DPState dState def)
   where
-    dState = emptyDState {_genDelegs = GenDelegs genDelegs0}
+    dState = def {_genDelegs = GenDelegs genDelegs0}
 
 -- | Implementation of abstract transaction size
 txsize :: Tx era -> Integer
@@ -1275,3 +1219,42 @@ returnRedeemAddrsToReserves es = es {esAccountState = acnt', esLState = ls'}
         }
     us' = us {_utxo = UTxO nonredeemers :: UTxO era}
     ls' = ls {_utxoState = us'}
+
+--------------------------------------------------------------------------------
+-- Default instances
+--------------------------------------------------------------------------------
+
+instance Default (PPUPState era) where
+  def = PPUPState emptyPPPUpdates emptyPPPUpdates
+
+instance Default (UTxOState era) where
+  def = UTxOState (UTxO Map.empty) (Coin 0) (Coin 0) def
+
+instance Default (EpochState era) where
+  def = EpochState def def def def def def
+
+instance Default (LedgerState era) where
+  def = LedgerState def def
+
+instance Default (DPState crypto) where
+  def = DPState def def
+
+instance Default (InstantaneousRewards crypto) where
+  def = InstantaneousRewards Map.empty Map.empty
+
+instance Default (DState crypto) where
+  def =
+    DState
+      Map.empty
+      Map.empty
+      biMapEmpty
+      Map.empty
+      (GenDelegs Map.empty)
+      def
+
+instance Default (PState crypto) where
+  def =
+    PState Map.empty Map.empty Map.empty
+
+instance Default AccountState where
+  def = AccountState (Coin 0) (Coin 0)

shelley/chain-and-ledger/executable-spec/src/Shelley/Spec/Ledger/PParams.hs

@@ -41,6 +41,7 @@ import Control.DeepSeq (NFData)
 import Control.Monad (unless)
 import Data.Aeson (FromJSON (..), ToJSON (..), (.!=), (.:), (.:?), (.=))
 import qualified Data.Aeson as Aeson
+import Data.Default.Class (Default, def)
 import Data.Foldable (fold)
 import Data.Functor.Identity (Identity)
 import Data.List (nub)
@@ -300,6 +301,9 @@ instance FromJSON (PParams era) where
         <*> obj .:? "minUTxOValue" .!= mempty
         <*> obj .:? "minPoolCost" .!= mempty
 
+instance Default (PParams era) where
+  def = emptyPParams
+
 -- | Returns a basic "empty" `PParams` structure with all zero values.
 emptyPParams :: PParams era
 emptyPParams =