root/trunk/examples/engines/engines.lgt

/*
This is a simple example of category composition, i.e. importation of 
categories by other categories in order to provide modified components 
for building objects, using car engines.

The example defines a car engine protocol (enginep), a standard engine 
(classic), and an improved version of it (sport). Both engines are then 
imported in two car models (sedan and coupe).
*/


% first we define a protocol for describing the characteristics of an engine:

:- protocol(enginep).

    :- public(reference/1).
    :- public(capacity/1).
    :- public(cylinders/1).
    :- public(horsepower_rpm/2).
    :- public(bore_stroke/2).
    :- public(fuel/1).

:- end_protocol.


% second, we can define a typical engine as a category, which will be used 
% when "assembling" cars:

:- category(classic,
    implements(enginep)).

    reference('M180.940').
    capacity(2195).
    cylinders(6).
    horsepower_rpm(94, 4800).
    bore_stroke(80, 72.8).
    fuel(gasoline).

:- end_category.


% next, we define a souped up version of the previous engine, which differs 
% from the standard one only in its reference and in its horsepower:

:- category(sport,
    extends(classic)).

    reference('M180.941').
    horsepower_rpm(HP, RPM) :-
        ^^horsepower_rpm(ClassicHP, ClassicRPM),
        HP is truncate(ClassicHP*1.23),
        RPM is truncate(ClassicRPM*0.762).

:- end_category.


% with engines (and other components), we may start "assembling" some cars:

:- object(sedan,
    imports(classic)).


:- end_object.


:- object(coupe,
    imports(sport)).


:- end_object.