Plutus: Ledger.Tx.Constraints

Got it ✅ I’ll enhance the tutorial with icons so it’s more visually engaging and easier to skim. I’ll use standard emoji-based icons since they render well in Markdown.

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Plutus: Ledger.Tx.Constraints

📑 Table of Contents

1. 🚀 Introduction

2. 🧩 Defining Constraints

3. 💳 Must-Pay Constraints for Specific Types of Addresses

4. 🔧 Off-Chain Only Constraints

5. 🔍 Queries on Constraints

6. 🏗️ Off-Chain Transaction Generation

7. 🔗 Combining Multiple Typed Scripts in One Transaction

8. 📦 Lookups

9. ⚠️ Deprecated Functions

10. 📘 Glossary of Terms

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1. 🚀 Introduction

The Ledger.Tx.Constraints module defines transaction constraints (TxConstraints), which are declarative rules for transactions.

• Off-chain (wallet/backend): Used to build transactions (mkTx).

• On-chain (validator): Used to verify that transactions meet rules (checkScriptContext).

This helps ensure correctness and reduces boilerplate transaction logic.

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2. 🧩 Defining Constraints

Constraints express conditions like payments, signatures, datums, and validity ranges.

Examples:

• mustPayToTheScriptWithDatumHash

• mustSpendAtLeast

• mustProduceAtLeast

• mustIncludeDatumInTx

👉 These can be combined into a TxConstraints set.

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3. 💳 Must-Pay Constraints for Specific Types of Addresses

🔹 Public Key Constraints

• mustPayToPubKey

• mustPayToPubKeyWithDatumHash

• mustPayToPubKeyWithInlineDatum

🔹 Script Constraints

• mustPayToOtherScriptWithDatumHash

• mustPayToOtherScriptWithInlineDatum

🔹 Reference Script Constraints

• mustPayToAddressWithReferenceScript

• mustPayToAddressWithReferenceValidator

These ensure correct value locking at addresses.

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4. 🔧 Off-Chain Only Constraints

Used only while constructing transactions:

• spendUtxosFromPlutusV1Script

• spendUtxosFromTheScript

• spendUtxosFromPlutusV2Script

They help collect UTxOs from validators with appropriate redeemers.

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5. 🔍 Queries on Constraints

Check feasibility of constraints:

• isSatisfiable – is the constraint set achievable?

• modifiesUtxoSet – must any satisfying transaction change the UTxO set?

Useful for contract debugging.

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6. 🏗️ Off-Chain Transaction Generation

🔹 Unbalanced Transactions

Constraints produce an UnbalancedTx, which must be balanced & signed.

🔹 mkTx Function

mkTx :: Params -> ScriptLookups a 
     -> TxConstraints (RedeemerType a) (DatumType a) 
     -> Either MkTxError UnbalancedTx

🔹 Errors

Possible errors:

• TxOutRefNotFound

• DatumNotFound

• DeclaredInputMismatch

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7. 🔗 Combining Multiple Typed Scripts in One Transaction

SomeLookupsAndConstraints lets you merge multiple constraint sets.

• mkSomeTx – builds a multi-script transaction.

• mkTxWithParams – same as mkTx with parameters.

👉 Enables cross-contract workflows.

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8. 📦 Lookups

ScriptLookups provide context:

• UTxOs → unspentOutputs

• Scripts → otherScript, plutusV2OtherScript

• Datums → otherData

• Keys → paymentPubKeyHash

Lookups link abstract constraints with actual ledger data.

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9. ⚠️ Deprecated Functions

Old functions (to avoid):

• mustPayToTheScript → use mustPayToTheScriptWithDatumHash

• mustPayToAddressWithDatum → use mustPayToAddressWithDatumHash

• mustValidateIn → use mustValidateInTimeRange

✅ Always use updated versions.

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10. 📘 Glossary of Terms

• TxConstraint – A single transaction rule.

• TxConstraints – A collection of multiple constraints.

• Datum – Data attached to outputs.

• Redeemer – Data used when spending outputs.

• UTxO – Unspent transaction output.

• ScriptLookups – Context for resolving constraints.

• UnbalancedTx – Draft transaction before balancing.

• Validity Interval – Slot/time range when a tx is valid.

• PaymentPubKeyHash – Identifies a wallet.

• Minting Policy – Script controlling token mint/burn.

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