Defining a domain

A domain definition looks like

$$\bf == \bf add \bf\{ \bf\}$$

or like

$$\bf == \bf add \bf\{ \bf\}$$

where in each case

• the first Identifier must be a new identifier,
• the second Identifier must refer to an existing category,
• the third Identifier, if present, must refer to an existing domain.

The inheritance mechanism will be discussed later.

The DomainBody starts with an attrib-statement, that is a statement of the form

$$\tt attrib \bf ( \bf ) \bf ;$$

and continues with a sequence of function definitions. A function definition looks like

$$\bf ( \bf ) \bf == \bf ;$$

or like

$$\bf ( \bf ) \bf == \bf\{ \bf\}$$

These function definitions must satisfy the category of the domain.

A sequence of formal parameters is a sequence of declarations of the form

separated by commas.

The goal of the attrib-statement is to declare the attributes of a value (or object) of the domain (or class) being defined. In the case of

• OddNumbers, each value has just one attribute which is an Integer,
• Word, each value has two attributes: a String called st and an Integer called le representing the length of this String.

Note that attrib is also used as a private creator. Public creators have to use attrib directly or indirectly in order to initialize a new value.