Overview

So far, we have worked only with the low-level untyped version of validator functions which use the BuiltinData type for its arguments. With typed validators, we can define our own types for validation arguments, simplifying things. These types still get compiled down to the low-level BuiltinData type, but our high-level code can be more understandable.

For typed validators, we will use the mkTypedValidator instead of the mkValidatorScript that we have been using so far. mkTypedValidator uses the ToData typeclass (https://intersectMBO.github.io/plutus-apps/main/plutus-ledger-api/html/Plutus-V2-Ledger-Api.html#t:ToData) to convert the given types to BuiltinData types. In Haddock, we can find that the instances for this typeclass are already defined for regular Haskell and Plutus types. In the case of using those basic types, we just need to create a new data type and make it an instance of the ValidatorTypes class (https://intersectMBO.github.io/plutus-apps/main/plutus-ledger/html/Ledger-Typed-Scripts.html#t:ValidatorTypes). The basic syntax for creating a validator type is as follows:

data ArbitraryValidatorTypeName

instance Scripts.ValidatorTypes ArbitraryValidatorTypeName where
  type instance DatumType ArbitraryValidatorTypeName = Slot       -- Datum type (basic Plutus)
  type instance RedeemerType ArbitraryValidatorTypeName = Integer -- Redeemer type (basic Haskell)

With a typed validator, we use our defined types for Datum and Redeemer instead of the BuiltinData so the type signature of the mkValidator changes. Besides using our defined types for Datum and Redeemer, it also now returns a Bool instead of a (), with True signifying successful validation and False signifying a failed one.

mkValidator :: Slot -> Integer -> Plutus.ScriptContext -> Bool
mkValidator = ...

Following that, we can create a typed validator with the validator we defined above using the Plutus.Script.Utils package:

{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE TypeFamilies #-}
...

import qualified Plutus.Script.Utils.Typed as PSU
import qualified Plutus.Script.Utils.V2.Typed.Scripts as PSU.V2

typedValidator :: PSU.TypedValidator ArbitraryValidatorTypeName
typedValidator = PSU.V2.mkTypedValidator @ArbitraryValidatorTypeName
    $$(PlutusTx.compile [|| mkValidator ||])
    $$(PlutusTx.compile [|| wrap ||])
    where
        wrap = PSU.mkUntypedValidator

PSU.TypedValidator is version agnostic, but we must use PSU.V2.mkTypedValidator if we want to compile to Plutus V2. We also need the {-# LANGUAGE TypeApplications #-} and {-# LANGUAGE TypeFamilies #-} extensions for the above syntax to work properly.

Creating Custom Data Types

If we want to create custom data types for our datum or redeemer, we must also create them as instances of the aforementioned ToData typeclass. We should simply use the PlutusTx.unstableMakeIsData on our defined datum/redeemer type. The difference between unstableMakeIsData and makeIsDataIndexed is that the latter ensures consistent indexing that is required to be specified and it is recommended to use makeIsDataIndexed in production because it ensures the same data structure results across different Plutus versions.

data ExampleDatum = ExampleDatumConstr {
    field1 :: Field1Type,
    field2 :: Field2Type
  }
PlutusTx.unstableMakeIsData ''ExampleDatum

The rest is the same, we just use our data type for the datum/redeemer types:

data ArbitraryValidatorTypeName

instance Scripts.ValidatorTypes ArbitraryValidatorTypeName where
  type instance DatumType ArbitraryValidatorTypeName = ExampleDatum -- Datum type (custom defined)
  type instance RedeemerType ArbitraryValidatorTypeName = Integer   -- Redeemer type (basic Haskell)