37.2.1 Object Declaration

An object object-identifier is declared by writing it in the following form:

     object-identifier :: {
             sentence-1 &
             sentence-2 &

where object-identifier is a Prolog term that is either an atom or a compound term of the form functor(V1,...,Vn), where V1,...,Vn are distinct variables. The object body consists of a number of sentences, possibly none, surrounded by braces, where each sentence is either a method-directive, to be executed when the object is created, or a method-clause. A method is a number of method-clauses with the same principal functor. A method-clause has a clausal syntax similar to that of Prolog, but instead of usual predicate calls in the body of a clause there are method-calls. Ordinary Prolog goals are also allowed in a prefixed form, using `:' as a prefix. A method-directive is a directive that contains method-calls.

All sentences are subject to term expansion (see Term and Goal Expansion, built-in predicate expand_term/2) before further processing, so in particular definite clause grammar syntax can be used in method-clauses. In addition, before expand_term/2, sentences are expanded by the predicate user:method_expansion/3.

method_expansion(+Term1,+ObjectIdentifier,?Term2) hook
Defines transformations on methods similarly as user:term_expansion/[2,4]. At the end of an object definition, user:method_expansion/3 is called with end_of_object.