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name: compact description: >- Write privacy-preserving smart contracts in Compact (Minokawa) for Midnight Network. Use when creating contracts, defining types, using standard library functions, or implementing ZK patterns. Triggers on Compact language, circuits, ledger state, hashing, or zero-knowledge contract questions. metadata: author: FractionEstate version: '0.18'

Compact Smart Contracts

Compact (being renamed to Minokawa) is Midnight's domain-specific language for privacy-preserving smart contracts. Contracts compile to ZK-SNARKs, enabling selective disclosure of data.

Note: As of compiler v0.26.0, the language is being renamed from "Compact" to "Minokawa" under the Linux Foundation Decentralized Trust. The toolchain commands still use compact.

Quick Start

Copypragma language_version 0.18;

export ledger message: Opaque<"string">;

export circuit setMessage(input: Opaque<"string">): [] {
  message = disclose(input);  // Makes private input public
}

Contract Structure

Every Compact contract has three parts:

1. Pragma - Language version (pragma language_version 0.18;)
2. Ledger - On-chain state declarations
3. Circuits - ZK-proven functions

Core Concepts

Privacy Model

Notes:

• Circuit arguments and witness returns are treated as potentially private (“witness data”).
• disclose(...) is a compiler acknowledgement: it does not itself publish anything, it just permits an expression to flow into public outputs (ledger writes / exported circuit returns / cross-contract comms).
• Only Opaque<"string"> and Opaque<"Uint8Array"> are currently supported.

Ledger Types

Copyledger counter: Counter;           // Auto-incrementing
ledger balances: Map<Bytes<32>, Uint<64>>;  // Key-value
ledger members: Set<Field>;        // Membership tracking
ledger tree: MerkleTree<20, Field>;  // Cryptographic proofs

Reference Files

Templates

Compilation

Copy# Compile contract
compact compile contracts/my-contract.compact contracts/managed/my-contract

# Output structure
contracts/managed/my-contract/
├── contract/    # JSON artifacts
├── keys/        # ZK proving/verifying keys
└── zkir/        # ZK Intermediate Representation

Common Errors

Best Practices

• ✅ Start with pragma language_version 0.18;
• ✅ Use witness for private inputs that need proofs
• ✅ Choose smallest Uint<N> that fits your data
• ✅ Use persistentHash for on-chain data, transientHash for temp
• ❌ Don't expose secrets via disclose() unnecessarily
• ❌ Avoid large state (increases gas costs)

Resources

• Writing a contract
• Language reference
• Explicit disclosure
• Compact standard library
• Ledger ADTs
• Opaque data types
• Examples Repository