Contract Structure

Contract Structure

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:
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main
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( txSkel : Zen.Types.txSkeleton )
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( context : Zen.Types.context )
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( contractId : Zen.Types.contractId )
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( command : string )
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( sender : Zen.Types.sender )
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( messageBody : option Zen.Types.data )
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( wallet : Zen.Types.wallet )
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( state : option Zen.Types.data )
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: Zen.Types.contractResult `Zen.Cost.t` n
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where n must be an expression which evaluates to a natural number (nat).

Parameters

    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:
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match command with
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| "redeem" -> redeem txSkeleton contractId returnAddress wallet
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| "buy" -> buy txSkeleton contractId returnAddress
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    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.

Output

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 None
      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.
Last modified 9mo ago