Transactions

Balzac provides a simple syntax to express Bitcoin transactions, which is summarized as follows:

transaction txName {
    input = ...
    output = ...
    absLock = ...   // optional
    relLock = ...   // optional
}

Inputs

The input field of a transaction specifies

  • the transaction output, that is a transaction and an output index;

  • the witnesses, that are the actual parameters with which the output script is evaluated.

The syntax to express the pair transaction output/witnesses is T@n : e1 e2 e3, where T is an expression of type transaction, n is an integer (not an expression), and e1 e2 e3 are the witnesses expressions whose type must match the type of the parameters of the transaction output script.

transaction A {
    ...
    output = 1 BTC : fun(n:int) . n == 42
}

transaction B {
    input = A@0 : 42
    ...
}

Generally, the input field can contain a list of T@n : wit, denoted by the list delimiters [...] and separated by ;. Moreover, @n can be omitted and the output index is assumed to be 0. For example:

transaction B {
    input = [
        A : 42;         // same of A@0 : 42
        A1@3 : sig(k)
    ]
    ...
}

See Expressions for details.

Outputs

The output field of a transaction specifies

  • the bitcoin amount, that is the value of the output;

  • the script, that is the condition that the redeeming transaction must satisfy.

The syntax to express the pair bitcoin amount/script is B : fun(x:TypeX,...,y:TypeY) . E, where B is an expression of type int, x and y are script parameters, TypeX and TypeY are types (e.g. int, string, …) and E is an expression of type boolean.

transaction A {
    ...
    output = 1 BTC : fun(n:int) . n == 42
}

Generally, the output field can contain a list of B : fun(x:TypeX,...,y:TypeY) . E, denoted by the list delimiters [...] and separated by ;. For example:

transaction A {
    ...
    output = [
        1 BTC : fun(x:int) . x == 42;
        0.5 BTC : fun(y:signature) . versig(k; y)
    ]
    ...
}

See Expressions for details.

AbsLock

The field absLock allows to specify when a transaction will be valid.

The time can be expressed in two ways:

  • absLock = block N
    where N is an expression of type int representing the block number at which the transaction will be valid
  • absLock = date D
    where D is an expression of type int representing the date (in seconds from 1970-01-01) at which the transaction will be valid.

The expressions N and D are subject to the same constraints of Absolute timelocks.

Refer to Dates and Delays for convenient ways for expressing dates.

RelLock

The field relLock allows to specify when a transaction will be valid.

The time can be expressed in two ways:

  • relLock = N block from T
    where N and T are expressions of type int and transaction respectively, representing the number of blocks from T at which the transaction will be valid
  • relLock = D from T
    where D and T are expressions of type int and transaction respectively, representing the seconds from T at which the transaction will be valid

The expressions N and D are subject to the same constraints of Relative timelocks, while the expression T must evaluate to one of the input transactions.

Refer to Dates and Delays for convenient ways for expressing delays.