A Script With Multiple Different Datum Types

Question

I have 4 different Datum Data Types in my script because for 4 different use cases in my script.

data FundCreationDatum = FundCreationDatum
  { vFundOwner :: PaymentPubKeyHash,
    vPrizeAmount :: Integer,
    vProjectLabel :: [BuiltinByteString],
    vPrizeDistributionRatio :: [Integer]
  }

data ProjectSubmitDatum = ProjectSubmitDatum
  { vProjectOwner :: PaymentPubKeyHash,
    vProjectRegistrationFee :: Integer,
    vProjectCategory :: BuiltinByteString,
    vFundPayIdentifier :: PaymentPubKeyHash
  }

data VotingActionDatum = VotingActionDatum
  { vProjectToVote :: PaymentPubKeyHash,
    vVoterPayAddress :: PaymentPubKeyHash,
    vAdaLovelaceValue :: Integer,
    vVoteFundIdentifier :: PaymentPubKeyHash,
    vActionName :: BuiltinByteString
  }
  deriving (Show)

data ConToMatchPool = ConToMatchPool
  { vFundAddress :: PaymentPubKeyHash,
    vPrizeFund :: Integer
  }
  deriving (Show)

I then bundled the 4 data types into a single data type with the Maybe monad.

data QuadraDatum = QuadraDatum
  { qCreateFund :: (Maybe FundCreationDatum),
    qVoting :: (Maybe VotingActionDatum),
    qSubProject :: (Maybe ProjectSubmitDatum),
    qContrPool :: (Maybe ConToMatchPool)
  }

I am trying to send a utxo with datum attached like this.

start cp = do 
  let dat = QuadraDatum qContrPool
            {vFundOwner = cpFundOwner cp
            ,vPrizeAmount = cpPrizeAmount cp
            ,vProjectLabel = cpProjectLabel cp
            ,vPrizeDistributionRatio = cpPrizeDistributionRatio cp
            }
      tx = Constraints.mustPayToTheScript dat $ Ada.lovelaceValueOf $ (cpPrizeAmount cp)  
  ledgerTx <- submitTxConstraints typedValidator tx
  void $ awaitTxConfirmed $ getCardanoTxId ledgerTx

I am getting the following error

 error:
    • Couldn't match expected type ‘Maybe FundCreationDatum’
                  with actual type ‘FundCreationDatum’

Answer 1

let's say we have a Maybe Integer type, then the value must be assigned as either Just 3 or Nothing.

Directly assigning it as 3 won't work.

So your QuadraDatum should be created as

  let dat = QuadraDatum 
              (Just qContrPool)
              (Just {vFundOwner = cpFundOwner cp
                  ,vPrizeAmount = cpPrizeAmount cp
                  ,vProjectLabel = cpProjectLabel cp
                  ,vPrizeDistributionRatio = cpPrizeDistributionRatio cp
               }) 
               Nothing
               Nothing

Also, better approach is to use multiple constructors something like this

data QuadraDatum = FundCreationDatum
  { 
    vPrizeAmount :: Integer,
    ...
  }|
  ProjectSubmitDatum
    { 
      vProjectRegistrationFee :: Integer,
      ...
    }
  deriving (Show)