An object object-identifier is declared by writing it in the following form:
object-identifier :: {
sentence-1 &
sentence-2 &
:
sentence-n
}.
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) hookuser:method_expansion(+Term1,+ObjectIdentifier,?Term2)
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.