Cardano Plutus and EUTxO Contracts

EUTxO — Cardano's Foundation

Cardano extends Bitcoin's UTXO model into the Extended UTXO (EUTxO) model. Each UTXO can carry arbitrary data ('datum') and is governed by a validator script ('validator'). When a transaction tries to spend a UTXO, the validator script runs: it has access to the UTXO's datum, the transaction's structure, and a 'redeemer' supplied by the spender. If the validator returns true, the spend is allowed; otherwise it's rejected. Smart contracts on Cardano are validators that govern UTXOs.

Plutus as the Language

Plutus is Cardano's smart-contract platform. The on-chain language is Plutus Core (a typed lambda calculus); the off-chain language is Haskell (or, more recently, languages that compile to Plutus Core like Aiken). Most developers write Haskell that compiles to Plutus Core; the strong type system catches many bugs at compile time. The trade-off: Haskell's small developer pool relative to Solidity. The benefit: extremely well-typed, formally analysable contracts.

EUTxO vs Account Model — The Big Difference

In Ethereum's account model, the state of, say, an AMM is one mapping in one contract. All swaps modify that mapping. In EUTxO, the AMM's state is distributed across many UTXOs. A user's swap creates a transaction that consumes specific UTXOs (representing pool state and user funds) and produces new ones. Two users can't swap concurrently on the same UTXO — only one transaction per UTXO per block. This produces real architectural differences in how DeFi protocols are designed on Cardano.

• Cardano = EUTxO model, contracts are validator scripts attached to UTXOs
• Plutus = on-chain language (Plutus Core), with Haskell as off-chain dev language
• Concurrency works differently — one transaction per UTXO per block
• Strong type system enables formal verification; smaller developer pool