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10.30.5.1 Syntax of Class Definitions

The following BNF grammar gives a concise description of the syntax of class definitions. It assumes an understanding of Prolog syntax for the following items: variable, atom, compound_term, and constant. Slot types, particularly the address, class and pointer types, were discussed in an earlier section.

class_def::= class_begin { clause | method } class_end
class_begin::= :- class class_name opt_class_spec .
opt_class_spec::= empty | = class_spec
class_spec::= multi_parent_or_slots | term_class_spec
clause::= head opt_body .
head::= atom | compound_term .
method::= message_head opt_body .
message_head::= message_goal
class_end::= :- end_class opt_class_name .
| empty /* if followed by class_begin or eof */
message::= atom | compound_term
multi_parent_or_slots::= parent_or_slots { + parent_or_slots }
parent_or_slots::= class_name | [] | [ slot_def {, slot_def } ]
slot_def::= opt_visibility slot_name : slot_type opt_init_value
opt_visibility::= empty | private | protected | public
opt_init_value::= empty | = constant
term_class_spec::= term(term opt_goal_essence)
opt_goal_essence::= empty | , goal opt_essence
opt_essence::= empty | , essence
essence::= [ variable : slot_type { , variable : slot_type } ]
opt_body::= empty | :- body
body::= message_or_goal { , message_or_goal }
message_or_goal::= message_goal | goal
message_goal::= variable message_operator message
message_operator::= << | >> | <-
opt_class_name::= empty | class_name
class_name::= atom
slot_name::= atom
slot_type::= integer
| short
| char
| unsigned_short
| unsigned_char
| float
| double
| atom
| address
| term
| class_name
| pointer(atom)


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