| title | author |
|---|---|
M09 - Going Live |
Walker Leite |
In this module we'll see how to use custom types in our validation script, something critical to build useful smart contracts. We'll also create some tests for the validator using Plutip.
To run this presentation type (you will need nix):
../../slide README.md- LovelaceAcademy Discord
- StackExchange (:bulb: use the tag lovelace-academy)
- Plutonomicon Discord
- Typeclasses (module 4)
- Building smart contracts (module 6)
- Cardano-transaction-lib (module 8)
import PlutusTx.Prelude (BuiltinData)
-- ...
validator :: BuiltinData -> BuiltinData -> BuiltinData -> ()
validator datum redeemer context = ()
validator' :: Validator
validator' = mkValidatorScript $$(compile [||validator||])
-- ...💡 Because
PlutusTx.compilefunction relies on TemplateHaskell, every definition that needs to be used inside it (on-chain code in our case) needs to have an inlinable pragma{-# INLINABLE definition -}.PlutusTx.Preludeexposes definitions with this pragma, in this case,BuiltinData.
-- ...
data Password = Password Integer
validator :: BuiltinData -> Password -> BuiltinData -> ()
validator _ (Password n) _ | n == 42 = ()
validator _ _ _ = _shouldFail
validator' :: Validator
validator' = mkValidatorScript $$(compile [||validator||])
-- ...Couldn't match type `Password` with `BuiltinData`
Expected type: template-haskell-2.16.0.0:Language.Haskell.TH.Syntax.Q
(template-haskell-2.16.0.0:Language.Haskell.TH.Syntax.TExp
(PlutusTx.Code.CompiledCode
(BuiltinData -> BuiltinData -> BuiltinData -> ())))
Actual type: th-compat-0.1.4:Language.Haskell.TH.Syntax.Compat.SpliceQ
(PlutusTx.Code.CompiledCode
(BuiltinData -> Password -> BuiltinData -> ()))
In the expression: compile [|| validator ||]
In the Template Haskell splice $$(compile [|| validator ||])
In the first argument of `mkValidatorScript`, namely
`$$(compile [|| validator ||])`
Found hole: _shouldFail :: ()
Or perhaps `_shouldFail` is mis-spelled, or not in scope
In the expression: _shouldFail
In an equation for `validator`: validator _ _ _ = _shouldFail
- How to fix the type error?
- How to tell to plutus core to fail?
The plutus runtime only accepts one result from the validator: () (which is the same as unit in PureScript). This is hard-coded as you can see in the expected type. When () is returned, it means script has been evaluated, when something wrong happens, anything, the script should throw an exception.
It means that we can use something like:
import PlutusTx.Prelude (BuiltinData, error)
-- error :: forall a. () -> a
validator :: BuiltinData -> BuiltinData -> BuiltinData -> ()
validator _ _ _ = error ()a is also know as undefined, something that can't be evaluated, trying to evaluate it at runtime will throw an exception.
data Data =
Constr Integer [Data]
| Map [(Data, Data)]
| List [Data]
| I Integer
| B BS.ByteString
deriving stock (Show, Eq, Ord, Generic)
deriving anyclass (NFData)
data BuiltinData = BuiltinData DataPlutusTx.Datais a Plutus Core version of a "JSON", with its type constructors you can build a tree of different nestedDatavalues. Plutus core runtime only knows aboutDatavalues. Datum, redeemer and script context values are allDatavalues.BuiltinDatais a INLINABLEDatawrapper for on-chain data.
More on Data type
We can build a validator function that uses any type using mkUntypedValidator.
import Plutus.Script.Utils.Typed (IsScriptContext (mkUntypedValidator))
validator' :: Validator
validator' = mkValidatorScript $$(compile [|| wrap ||])
where
wrap = mkUntypedValidator _validatorclass UnsafeFromData sc => IsScriptContext sc where
{-# INLINABLE mkUntypedValidator #-}
mkUntypedValidator
:: (UnsafeFromData d, UnsafeFromData r)
=> (d -> r -> sc -> Bool)
-> UntypedValidatord, r and sc represents the datum, redeemer and script context types. Bool is hardcoded, so if the validator evaluates it should return True, False otherwise.
We have a default ScriptContext that fullfill the sc hole, available in Plutus.V1.Ledger.Api and Plutus.V2.Ledger.Api.
import Plutus.V2.Ledger.Api (Validator, ScriptContext, mkValidatorScript)
import Plutus.Script.Utils.Typed (IsScriptContext (mkUntypedValidator))
newtype Password = Password Integer
validator :: BuiltinData -> Password -> ScriptContext -> Bool
validator _ (Password n) _ | n == 42 = True
validator _ _ _ = error ()
validator' :: Validator
validator' = mkValidatorScript $$(compile [|| wrap ||])
where
wrap = mkUntypedValidator validatorNo instance for (PlutusTx.IsData.Class.UnsafeFromData Password)
arising from a use of `mkUntypedValidator`
In the expression: mkUntypedValidator validator
In an equation for `wrap`: wrap = mkUntypedValidator validator
In an equation for `validator'`:
validator'
= mkValidatorScript $$(compile [|| wrap ||])
where
wrap = mkUntypedValidator validator
wrap = mkUntypedValidator validator
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
As you can see BuiltinData has an instance for UnsafeFromData, but not Password.
import PlutusTx (UnsafeFromData (unsafeFromBuiltinData))
import PlutusTx.Builtins.Internal (BuiltinData (BuiltinData), unsafeDataAsI)
import Plutus.V2.Ledger.Api (Validator, ScriptContext, mkValidatorScript)
import Plutus.Script.Utils.Typed (IsScriptContext (mkUntypedValidator))
newtype Password = Password Integer
instance UnsafeFromData Password where
unsafeFromBuiltinData d = Password (unsafeDataAsI d)
unsafeFromBuiltinData _ = error ()
validator :: BuiltinData -> Password -> ScriptContext -> Bool
validator _ (Password n) _ | n == 42 = True
validator _ _ _ = error ()
validator' :: Validator
validator' = mkValidatorScript $$(compile [|| wrap ||])
where
wrap = mkUntypedValidator validator💡 Unsafe terminlogy here means that the type conversion can fail unexpectedly, which will trigger a validator error at runtime. We need to be sure what we're passing to validator is correct. You can also use the safer alternative
FromDatawhich returns aMaybe a, but you'll need more boilerplate.
Is a template haskell function that creates the instance by reading the type signature of the given type.
{-# OPTIONS_GHC -ddump-splices #-}
-- ...
newtype Password = Password Integer
unstableMakeIsData ''Password
{- GHC output:
Splicing declarations
unstableMakeIsData ''Password
====>
instance PlutusTx.IsData.Class.ToData Password where
{-# INLINABLE PlutusTx.IsData.Class.toBuiltinData #-}
PlutusTx.IsData.Class.toBuiltinData (Password arg_a9wO)
= (PlutusTx.Builtins.Internal.mkConstr 0)
...
instance PlutusTx.IsData.Class.FromData Password where
{-# INLINABLE PlutusTx.IsData.Class.fromBuiltinData #-}
PlutusTx.IsData.Class.fromBuiltinData d_a9wP
= let
...
in
...
instance UnsafeFromData Password where
{-# INLINABLE unsafeFromBuiltinData #-}
unsafeFromBuiltinData d_a9wY
= let
...
in
...
-}
validator :: BuiltinData -> Password -> ScriptContext -> Bool
validator _ (Password n) _ | n == 42 = True
validator _ _ _ = error ()The optional dump-splice flag is being used to print the code generated by unstableMakeIsData.
💡 In haskell a preceding ' means "elevates this definition in the kind level" and '' means "elevates this definition in the template level".
As a donator I want to lock 10 ADA in the contract
Given that I have fulfilled the correct answer, which is 42, as a visitor I want to get all ADA in the contract
mkdir modules/M09-going-live/{contract,dapp}
(
cd modules/M09-going-live/contract
nix flake init -t github:LovelaceAcademy/nix-templates#hix-plutus
)
(
cd modules/M09-going-live/dapp
nix flake init -t github:LovelaceAcademy/nix-templates#pix-ctl-full
)