2. Objects

An object is specified by an object-descriptor:

super
   Item1
   Item2
   ...
   Itemn

where super is an optional super pattern – if no super is specified, then the object is a subpattern of pattern Object. Pattern Object is the top superpattern in the pattern- and object hierarchy.

The main-part of an object is a list of Items, Item1, Item2, …, Itemn.

An Item is either a Declaration or a Statement.

There must be exactly one item per line, and all the items must be indented to the same level.

Objects may be nested in which case the indentation level determines the nesting levels – see the section on block-structure.

Example

Record
   name: ref  String
   age: var Integer
   spouse: ref Person
   isMarried -> B: var Boolean:
      B := spouse <> none

The superpattern of this object is Record. The object has 4 Items: name, age, spouse, and isMarried.

Alternative syntax

Instead of using indentation and line shifts to define the block levels and separation between statements, it is possible to use curly brackets and semicolon:

super{Item1; Item2; ... Itemsn }

Examples

Record{ name: ref String; age: var Integer }

Record{
   name: ref  String;
   age: var Integer;
   spouse: ref Person;
   isMarried -> B: var Boolean:{ B := spouse <> none }
}

Grammar

The grammar for an object is as follows. It is defined using curly brackets and semicolon, but as mentioned, indentation and line shifts may be used instead.

<ObjectDescriptor> ::= [ <Super> ] '{' <Items> '}'
<Items> ::= empty | <Item> { ';' <Item> }