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std.compact ∙ README ∙ API

API

Structs​

Maybe​

Encapsulates an optionally present value. If is_some is false, value should be null(a) by convention.

export struct Maybe[a] {
  is_some: Boolean;
  value: a;
}

Either​

Disjoint union of a and b. Iff is_left if true, left should be populated, otherwise right. The other should be null(_) by convention.

export struct Either[a, b] {
  is_left: Boolean;
  left: a;
  right: b;
}

CurvePoint​

A point on the proof systems embedded curve, in affine coordinates.

Only outputs of elliptic curve operations are actually guaranteed to lie on the curve.

export struct CurvePoint {
  x: Field;
  y: Field;
}

MerkleTreeDigest​

The root hash of a Merkle tree, represented by a single Field.

export struct MerkleTreeDigest { field: Field; }

MerkleTreePathEntry​

An entry in a Merkle tree path, indicating if the path leads left or right, and the root of the sibling node. Primarily used in MerkleTreePath

export struct MerkleTreePathEntry {
  sibling: MerkleTreeDigest;
  goes_left: Boolean;
}

MerkleTreePath​

A path in a depth n Merkle tree, leading to a leaf of type a. Primarily used for merkle_tree_path_root.

This can be constructed from witnesses that use the compiler output's find_path_for_leaf and path_for_leaf functions.

export struct MerkleTreePath[n, a] {
  leaf: a;
  path: Vector[n, MerkleTreePathEntry];
}

ContractAddress​

The address of a contract, used as a recipient in send, send_immediate, create_zswap_output, and mint_token.

export struct ContractAddress { bytes: Bytes[32]; }

CoinInfo​

The description of a newly created coin, used in outputting coins, or spending/receiving coins that originate in the current transaction.

nonce can be deterministically derived with evolve_nonce.

Used in:

export struct CoinInfo {
  nonce: Bytes[32];
  color: Bytes[32];
  value: Unsigned Integer[64];
}

QualifiedCoinInfo​

The description of an existing coin in the ledger, ready to be spent.

Used in:

export struct QualifiedCoinInfo {
  nonce: Bytes[32];
  color: Bytes[32];
  value: Unsigned Integer[64];
  mt_index: Unsigned Integer[64];
}

ZswapCoinPublicKey​

The public key used to output a CoinInfo to a user, used as a recipient in send, send_immediate, and create_zswap_output.

export struct ZswapCoinPublicKey { bytes: Bytes[32]; }

SendResult​

The output of send and send_immediate, detailing the created coin, and the change from spending the input, if applicable.

export struct SendResult {
  change: Maybe[CoinInfo];
  sent: CoinInfo;
}

Circuits​

some​

Constructs a Maybe[a] containing an element of type a

export circuit some[a](value: a): Maybe[a];

none​

Constructs a Maybe[a] containing nothing

export circuit none[a](): Maybe[a];

left​

Construct an Either[a, b] containing the a item of the disjoint union

export circuit left[a, b](value: a): Either[a, b];

Constructs an Either[a, b] containing the b item of the disjoint union

export circuit right[a, b](value: b): Either[a, b];

transient_hash​

Builtin transient hash compression function

This function is a circuit-efficient compression function from field elements to field elements, which is not guaranteed to persist between upgrades. It should not be used to derive state data, but can be used for consistency checks.

export circuit transient_hash(x: Field, y: Field): Field;

transient_commit​

Builtin transient commitment function

This function is a circuit-efficient commitment function over arbitrary types, and a field element commitment opening, to field elements, which is not guaranteed to persist between upgrades. It should not be used to derive state data, but can be used for consistency checks.

export circuit transient_commit[a](value: a, rand: Field): Field;

persistent_hash​

Builtin persistent hash compression function

This function is a non-circuit-optimised compression function from two 256-bit bytestrings to one 256-bit bytestring. It is guaranteed to persist between upgrades, with the exception of devnet, where this function is provided, but mocked using transient_hash. It should be used to derive state data, and not for consistency checks where avoidable.

export circuit persistent_hash(x: Bytes[32], y: Bytes[32]): Bytes[32];

persistent_commit​

Builtin persistent commitment function

This function is a non-circuit-optimised commitment function from arbitrary values representable in Compact, and a 256-bit bytestring opening, to a 256-bit bytestring. It is guaranteed to persist between upgrades, with the exception of devnet, where this function is provided, but mocked using transient_commit. It should be used to derive state data, and not for consistency checks where avoidable.

export circuit persistent_commit[a](value: a, rand: Bytes[32]): Bytes[32];

degrade_to_transient​

This function "degrades" the output of a persistent_hash or persistent_commit to a field element, which can then be used in transient_hash or transient_commit.

export circuit degrade_to_transient(x: Bytes[32]) : Field;

ec_add​

This function add two elliptic CurvePoints (in multiplicative notation)

export circuit ec_add(a: CurvePoint, b: CurvePoint): CurvePoint;

ec_mul​

This function multiplies an elliptic CurvePoint by a scalar (in multiplicative notation)

export circuit ec_mul(a: CurvePoint, b: Field): CurvePoint;

ec_mul_generator​

This function multiplies the primary group generator of the embedded curve by a scalar (in multiplicative notation)

export circuit ec_mul_generator(b: Field): CurvePoint;

hash_to_curve​

This function maps arbitrary types to CurvePoints.

Outputs are guaranteed to have unknown discrete logarithm with respect to the group base, and any other output, but are not guaranteed to be unique (a given input can be proven correct for multiple outputs).

Inputs of different types a may have the same output, if they have the same field-aligned binary representation.

export circuit hash_to_curve[a](value: a): CurvePoint;

merkle_tree_path_root​

Derives the Merkle tree root of a MerkleTreePath, which should match the root of the tree that this path originated from.

export circuit merkle_tree_path_root[n, a](path: MerkleTreePath[n, a]): MerkleTreeDigest;

native_token​

Returns the token type of the native token

export circuit native_token(): Bytes[32];

token_type​

Transforms a domain seperator for the given contract into a globally namespaced token type. A contract can issue tokens for its domain seperators, which lets it create new tokens, but due to collision resistance, it cannot mint tokens for another contract's token type. This is used as the color field in CoinInfo.

export circuit token_type(domain_sep: Bytes[32], contract: ContractAddress): Bytes[32];

mint_token​

Creates a new coin, minted by this contract, and sends it to the given recipient. Returns the corresponding CoinInfo. This requires inputting a unique nonce to function securely, it is left to the user how to produce this.

export circuit mint_token(
  domain_sep: Bytes[32],
  value: Unsigned Integer[64],
  nonce: Bytes[32],
  recipient: Either[ZswapCoinPublicKey, ContractAddress]
): CoinInfo;

evolve_nonce​

Deterministically derives a CoinInfo nonce from a counter index, and a prior nonce.

export circuit evolve_nonce(
  index: Unsigned Integer[64],
  nonce: Bytes[32]
): Bytes[32];

burn_address​

Returns a payment address that guarantees any coins sent to it are burned.

export circuit burn_address(): Either[ZswapCoinPublicKey, ContractAddress];

receive​

Receives a coin, adding a validation condition requiring this coin to be present as an output addressed to this contract, and not received by another call

export circuit receive(coin: CoinInfo): Void;

send​

Sends given value from a coin owned by the contract to a recipient. Any change is returned and should be managed by the contract.

Note that this does not currently create coin ciphertexts, so sending to a user public key except for the current user will not lead to this user being informed of the coin they've been sent.

export circuit send(input: QualifiedCoinInfo, recipient: Either[ZswapCoinPublicKey, ContractAddress], value: Unsigned Integer[64]): SendResult;

send_immediate​

Like send, but for coins created within this transaction

export circuit send_immediate(input: CoinInfo, target: Either[ZswapCoinPublicKey, ContractAddress], value: Unsigned Integer[64]): SendResult;

merge_coin​

Takes two coins stored on the ledger, and combines them into one

export circuit merge_coin(a: QualifiedCoinInfo, b: QualifiedCoinInfo): CoinInfo;

merge_coin_immediate​

Takes one coin stored on the ledger, and one created within this transaction, and combines them into one

export circuit merge_coin_immediate(a: QualifiedCoinInfo, b: CoinInfo): CoinInfo;

Witnesses​

own_public_key​

Returns the ZswapCoinPublicKey of the end-user creating this transaction.

export witness own_public_key(): ZswapCoinPublicKey;

create_zswap_input​

Notifies the context to create a new Zswap input originating from this call. Should typically not be called manually, prefer send and send_immediate instead.

export witness create_zswap_input(coin: QualifiedCoinInfo): Void;

create_zswap_output​

Notifies the context to create a new Zswap output originating from this call. Should typically not be called manually, prefer send and send_immediate, and receive instead.

export witness create_zswap_output(coin: CoinInfo, recipient: Either[ZswapCoinPublicKey, ContractAddress]): Void;