Clarity, the smart contract language for the Stacks blockchain, is designed to optimise security, static analysis and transparency.

Clarity is an interpreted functional language that has no compilation to bytecode. This means:

The code is transparent — you can read exactly what the code will do on-chain.
There is no compiler-induced ambiguity — no unexpected low-level behaviour.

It lacks traditional object-oriented programming features like class inheritance, but it does support polymorphism through traits (see for example the SIP-009/NFT and SIP-010/FT trait definitions) which enable flexible and secure patterns for interacting with interchangeable contracts.

In this blog post, we'll explore the powerful concept of polymorphism in Clarity and show how it is achieved using traits, using real world examples taken from BigMarket DAO.

What Is a Trait in Clarity?

A trait is like an interface — it defines a contract's required functions and their signatures. Other contracts can implement these traits, and once implemented, they can be passed around and called dynamically using contract-call?.

This makes polymorphism possible: code can operate on any contract that implements a trait, without knowing its internal structure.

Example 1: Polymorphic Proposals in BigMarket DAO

BigMarket DAO uses a trait to allow the core DAO logic to interact with any kind of proposal, so long as it implements the standard interface:

(define-trait proposal-trait
  ((execute (principal) (response bool uint)))
)

The bigmarket-dao core contract then defines a generic execution function:

(use-trait proposal-trait 'SP3JP0N1ZXGASRJ0F7QAHWFPGTVK9T2XNXDB908Z.proposal-trait.proposal-trait)
...
(define-public (execute (proposal <proposal-trait>) (sender principal))
  (begin
    (try! (is-self-or-extension))
    (asserts! (map-insert executed-proposals (contract-of proposal) stacks-block-height) err-already-executed)
    (print {event: "execute", proposal: proposal})
    (as-contract (contract-call? proposal execute sender))
  )
)

Any contract that implements proposal-trait can be passed into this method and executed. This allows governance proposals to be modular and extensible without changing the core DAO logic.

Here’s an example of a DAO proposal on BigMarket

(impl-trait  'SP3JP0N1ZXGASRJ0F7QAHWFPGTVK9T2XNXDB908Z.proposal-trait.proposal-trait)

(define-public (execute (sender principal))
    (begin
        (try! (contract-call? .bme022-0-market-gating set-merkle-root-by-principal .bme023-0-market-predicting 0x6cf941784773751b4c0f4f887f25121106b2b59d026b5bc52822953f9c0e5fef))
        (try! (contract-call? .bme022-0-market-gating set-merkle-root-by-principal .bme023-0-market-scalar-pyth 0x6cf941784773751b4c0f4f887f25121106b2b59d026b5bc52822953f9c0e5fef))
        (try! (contract-call? .bme022-0-market-gating set-merkle-root-by-principal .bme023-0-market-bitcoin 0x6cf941784773751b4c0f4f887f25121106b2b59d026b5bc52822953f9c0e5fef))

        (print "Merkle root for account gating updated.")
        (ok true)
    )
)

In this example the proposal contract is passed as a trait-typed argument allowing its execute method to be called without knowing anything else about the specific contract - thus enabling the powerful feature of polymorphic contract calls

Note: DAO proposals in the Executor framework can only be registered via an on-chain proposal mechanism. While several such mechanisms are live in the Stacks ecosystem, each project is free to choose its own approach for gating proposal submission and execution. This design choice allows the Executor DAO framework to remain fully polymorphic in structure, while staying agnostic to the specific governance model implemented by any given project.

Example 2: Prediction Markets and Market Voting

BigMarket DAO supports different kinds of prediction markets — categorical, scalar, and even Bitcoin-backed. Rather than hardcode logic for each, the market-voting contract interacts with them polymorphically via a shared trait:

(define-trait prediction-market-trait
  ((dispute-resolution (uint principal) (response bool uint))
   (resolve-market-vote (uint uint) (response bool uint)))
)

The market voting logic becomes:

(use-trait prediction-market-trait .prediction-market-trait.prediction-market-trait)
...
(define-public (create-market-vote (market <prediction-market-trait>) ...)
  (begin
    (try! (as-contract (contract-call? market dispute-resolution ...)))
    ;; Logic continues...
  )
)

The market argument can be any contract that implements the prediction-market-trait. This abstraction allows new market types to be integrated without modifying the voting system.

In BigMarket, our scalar, categorical, and Bitcoin-native markets all implement dispute-resolution and resolve-market-vote, the details on how they implement this function is contract specific and of no concern to the voting contract which simply needs to start a vote.

Benefits of Trait-Based Polymorphism

Security: All implementations are statically checked at compile-time.
Extensibility: New functionality can be added via new contracts that implement existing traits.
Modularity: DAO and voting logic remain clean and general-purpose.
Dynamic contract tracking: By converting traits to principals via contract-of, you can store them in maps for whitelisting, discovery, or metadata lookup.

Final Thoughts

Polymorphism via traits is a powerful design pattern in Clarity, enabling DAOs like BigMarket to scale with complexity while maintaining security and simplicity. If you're building with Clarity, embracing traits isn't just useful — it's essential.

Want to see it in action? Check out the BigMarket DAO repository for live implementations. To start your own DAO project or dive deeper, check out the Executor DAO framework.

Follow the author on X: @mijoco_btc

Polymorphism in Clarity: Real-World Trait-Based Examples from BigMarket DAO