Add trivial example Plutus scripts to the API

And also as concrete data files in the repo.

These scripts always succeed, or always fail, so are only useful for
quick sanity tests.

cardano-api/src/Cardano/Api.hs

@@ -335,6 +335,8 @@ module Cardano.Api (
 
     -- ** Plutus scripts
     PlutusScript,
+    examplePlutusScriptAlwaysSucceeds,
+    examplePlutusScriptAlwaysFails,
 
     -- ** Script data
     ScriptData(..),

cardano-api/src/Cardano/Api/Script.hs

@@ -56,6 +56,8 @@ module Cardano.Api.Script (
 
     -- * The Plutus script language
     PlutusScript(..),
+    examplePlutusScriptAlwaysSucceeds,
+    examplePlutusScriptAlwaysFails,
 
     -- * Script data
     ScriptData(..),
@@ -105,6 +107,7 @@ import qualified Data.Text as Text
 import qualified Data.Text.Encoding as Text
 import           Data.Type.Equality (TestEquality (..), (:~:) (Refl))
 import           Data.Typeable (Typeable)
+import           Numeric.Natural (Natural)
 
 import           Data.Aeson (Value (..), object, (.:), (.=))
 import qualified Data.Aeson as Aeson
@@ -137,6 +140,7 @@ import qualified Cardano.Ledger.Alonzo.Language as Alonzo
 import qualified Cardano.Ledger.Alonzo.Scripts as Alonzo
 
 import qualified Plutus.V1.Ledger.Api as Plutus
+import qualified Plutus.V1.Ledger.Examples as Plutus
 
 import           Cardano.Api.Eras
 import           Cardano.Api.HasTypeProxy
@@ -1009,6 +1013,49 @@ instance (IsPlutusScriptLanguage lang, Typeable lang) =>
         PlutusScriptV1 -> "PlutusScriptV1"
 
 
+-- | An example Plutus script that always succeeds, irrespective of inputs.
+--
+-- For example, if one were to use this for a payment address then it would
+-- allow anyone to spend from it.
+--
+-- The exact script depends on the context in which it is to be used.
+--
+examplePlutusScriptAlwaysSucceeds :: WitCtx witctx
+                                  -> PlutusScript PlutusScriptV1
+examplePlutusScriptAlwaysSucceeds =
+    PlutusScriptSerialised
+  . Plutus.alwaysSucceedingNAryFunction
+  . scriptArityForWitCtx
+
+-- | An example Plutus script that always fails, irrespective of inputs.
+--
+-- For example, if one were to use this for a payment address then it would
+-- be impossible for anyone to ever spend from it.
+--
+-- The exact script depends on the context in which it is to be used.
+--
+examplePlutusScriptAlwaysFails :: WitCtx witctx
+                               -> PlutusScript PlutusScriptV1
+examplePlutusScriptAlwaysFails =
+    PlutusScriptSerialised
+  . Plutus.alwaysFailingNAryFunction
+  . scriptArityForWitCtx
+
+-- | The expected arity of the Plutus function, depending on the context in
+-- which it is used.
+--
+-- The script inputs consist of
+--
+-- * the optional datum (for txins)
+-- * the redeemer
+-- * the Plutus representation of the tx and environment
+--
+scriptArityForWitCtx :: WitCtx witctx -> Natural
+scriptArityForWitCtx WitCtxTxIn  = 3
+scriptArityForWitCtx WitCtxMint  = 2
+scriptArityForWitCtx WitCtxStake = 2
+
+
 -- ----------------------------------------------------------------------------
 -- Conversion functions
 --

scripts/plutus/always-fails-mint.plutus

@@ -0,0 +1,5 @@
+{
+    "type": "PlutusScriptV1",
+    "description": "An example Plutus script (for minting context) that always fails",
+    "cborHex": "4701000020020061"
+}

scripts/plutus/always-fails-stake.plutus

@@ -0,0 +1,5 @@
+{
+    "type": "PlutusScriptV1",
+    "description": "An example Plutus script (for stake context) that always fails",
+    "cborHex": "4701000020020061"
+}

scripts/plutus/always-fails-txin.plutus

@@ -0,0 +1,5 @@
+{
+    "type": "PlutusScriptV1",
+    "description": "An example Plutus script (for tx in context) that always fails",
+    "cborHex": "49010000200200200601"
+}

scripts/plutus/always-succeeds-mint.plutus

@@ -0,0 +1,5 @@
+{
+    "type": "PlutusScriptV1",
+    "description": "An example Plutus script (for minting context) that always succeeds",
+    "cborHex": "4a01000020020020000101"
+}

scripts/plutus/always-succeeds-stake.plutus

@@ -0,0 +1,5 @@
+{
+    "type": "PlutusScriptV1",
+    "description": "An example Plutus script (for stake context) that always succeeds",
+    "cborHex": "4a01000020020020000101"
+}

scripts/plutus/always-succeeds-txin.plutus

@@ -0,0 +1,5 @@
+{
+    "type": "PlutusScriptV1",
+    "description": "An example Plutus script (for tx in context) that always succeeds",
+    "cborHex": "4b0100002002002002000011"
+}