Data types

A data type is defined using deftype. A data type corresponds to an integer or Boolean value, although it could also be a composite construct like a record or structure (from software programming languages). The syntax is similar to a process, and the constraints about declarations/etc. apply here as well.

Often data types have some additional structure that is not required for a process. In particular, the body of the data type and its type signature provide information that relates a user-defined data type to a previously defined or built-in data type. When a user-defined data type is specified, a method for setting the value of the data type and reading its value must also be specified. If omitted, certain features of data types will not be enabled for the defined type.

The following is a simple example of a datatype that creates a dual-rail representation for a Boolean variable. The first line specifies that d1of2 is a new data type, and it implements the built-in type int<1>—a one-bit integer.

deftype d1of2 <: int<1> (bool d0,d1)
{
  spec {
    exclhi(d0,d1)
  }
}

The body of the type is similar to a process, except it can only contain connections, spec bodies, and special methods. The following would result in an error:

deftype d1of2 <: int<1> (bool d0,d1)
{
  bool p;
  spec {
    exclhi(d0,d1)
  }
}
-[ERROR]-> Expecting bnf-item `methods_body', got `bool'

Port lists for data types can be either built-in data types or user-defined data types. Channels (built-in or user-defined) and processes are not valid types for ports of a data type, since a data type is supposed to represent a circuit structure that is used to represent a data value.