Each contract must contain 2 functions: main and cf.
The main function is run whenever a contract is used within a transaction.
The function will run both at the validation and at the generation of the transaction.
The structure of the main function is:
main( txSkel : Zen.Types.txSkeleton )( context : Zen.Types.context )( contractId : Zen.Types.contractId )( command : string )( sender : Zen.Types.sender )( messageBody : option Zen.Types.data )( wallet : Zen.Types.wallet )( state : option Zen.Types.data ): Zen.Types.contractResult `Zen.Cost.t` n
where n must be an expression which evaluates to a natural number (nat).
txSkel : Zen.Types.txSkeleton : The partial transaction supplied as input to the contract.
context : Zen.Types.context : The blockchain context of the transaction, given by blockNumber (unsigned 32 bit integer), and timestamp - which is the UNIX Epoch time (unsigned 64 bit integer) of the block creation.
contractId : Zen.Types.contractId : The contract identifier. (version, hash)
command : string : String that the contract may use. Contains a command which tells the contract what to do. For example:
match command with| "redeem" -> redeem txSkeleton contractId returnAddress wallet| "buy" -> buy txSkeleton contractId returnAddress
sender : Zen.Types.sender : The sender identity. Can be any of the following:
Contract of Zen.Types.contractId: a contract, given by its ID
PK of Zen.Types.publicKey: a Public key
Anonymous: an anonymous sender
messageBody : option Zen.Types.data : The transaction may carry a message which can be any of the following:
Byte: of FStar.UInt8.t: 8 bit unsigned integer
U32 of FStar.UInt32.t: 32 bit unsigned integer
U64 of FStar.UInt64.t: 64 bit unsigned integer
I64 of FStar.Int64.t: 64 bit signed integer
ByteArray of Zen.Array.t FStar.UInt8.t: array of 8 bit unsigned integer
String of string: FStar.prims
Hash of Zen.Types.hash: 256-bit hash value
Lock of Zen.Types.lock: Lock
Signature of Zen.Types.signature: Signature
PublicKey of Zen.Types.publicKey: Public key
Collection of Zen.Types.dataCollection: Data collection
wallet : Zen.Types.wallet : Contains all the transaction inputs that were previously locked to the contract. In order for a contract to spend its own funds they need to come from contract wallet.
state : option Zen.Types.data : The contract current state. Can be either Some data (as the message body) or None.
The output of the contract is of the record type Zen.Types.contractReturn which has 3 fields:
state : Zen.Types.stateUpdate State update. Can be any of the following:
Delete - Delete the current state, resetting it to
NoChange - Keeping the current state as it is, with no change.
Update of Zen.Types.data - Change the state to be the new given data.
tx : Zen.Types.txSkeleton The generated transaction structure.
message : option Zen.Types.message An optional message for invoking another contract. This is a record type which has 3 fields:
recipient: Zen.Types.contractId - The recipient contract.
command: string - The command given to the recipient contract.
body: option Zen.Types.data - The message body of given to the recipient contract.