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/* This example illustrates how to associate a set of predicates with a
compound term. Parameters can be accessed from within an object by
using the execution-context built-in methods this/1 and parameter/2;
both alternatives are illustrated below.
*/
/* The first two parametric objects represent time and date values as
compound terms using the object's identifiers.
*/
:- object(date(_Year, _Month, _Day)).
:- info([
version is 1.1,
author is 'Paulo Moura',
date is 2005/9/5,
comment is 'Dates as parametric objects.',
parnames is ['Year', 'Month', 'Day']]).
:- public(year/1).
:- mode(year(?integer), one).
:- public(month/1).
:- mode(month(?integer), one).
:- public(day/1).
:- mode(day(?integer), one).
:- public(today/0).
:- mode(today, one).
:- public(leap_year/0).
:- mode(leap_year, zero_or_one).
year(Year) :-
parameter(1, Year).
month(Month) :-
parameter(2, Month).
day(Day) :-
parameter(3, Day).
today :-
{'$lgt_current_date'(Year, Month, Day)}, % defined in the config files
parameter(1, Year),
parameter(2, Month),
parameter(3, Day).
/* Alternative predicate definitions using this/1 instead of parameter/2
(see the User Manual for the pros and cons of both alternatives):
year(Year) :-
this(date(Year, _, _)).
month(Month) :-
this(date(_, Month, _)).
day(Day) :-
this(date(_, _, Day)).
today :-
{'$lgt_current_date'(Year, Month, Day)}, % defined in the config files
this(date(Year, Month, Day)).
*/
leap_year :-
parameter(1, Year),
(0 =:= mod(Year, 4), 0 =\= mod(Year, 100)
;
0 =:= mod(Year, 400)),
!.
:- end_object.
:- object(time(_Hours, _Mins, _Secs)).
:- info([
version is 1.1,
author is 'Paulo Moura',
date is 2005/9/5,
comment is 'Time as parametric objects.',
parnames is ['Hours', 'Mins', 'Secs']]).
:- public(hours/1).
:- mode(hours(?integer), one).
:- public(mins/1).
:- mode(mins(?integer), one).
:- public(secs/1).
:- mode(secs(?integer), one).
:- public(now/0).
:- mode(now, one).
hours(Hours) :-
parameter(1, Hours).
mins(Mins) :-
parameter(2, Mins).
secs(Secs) :-
parameter(3, Secs).
now :-
{'$lgt_current_time'(Hours, Mins, Secs)}, % defined in the config files
parameter(1, Hours),
parameter(2, Mins),
parameter(3, Secs).
/* Alternative predicate definitions using this/1 instead of parameter/2
(see the User Manual for the pros and cons of both alternatives):
hours(Hours) :-
this(time(Hours, _, _)).
mins(Mins) :-
this(time(_, Mins, _)).
secs(Secs) :-
this(time(_, _, Secs)).
now :-
{'$lgt_current_time'(Hours, Mins, Secs)}, % defined in the config files
this(time(Hours, Mins, Secs)).
*/
:- end_object.
/* The following parametric object illustrates a solution for implementing
modifiable object state. The idea is to represent object state by using
object parameters, defining "setter" predicates/methods that return the
updated object identifier.
*/
:- object(rectangle(_width, _height, _x, _y)).
:- info([
version is 1.0,
author is 'Paulo Moura',
date is 2005/9/5,
comment is 'A simple implementation of a geometric rectangle using parametric objects.',
parnames is ['Width', 'Height', 'X', 'Y']]).
:- public(init/0).
:- mode(init, one).
:- info(init/0,
[comment is 'Initialize rectangle position.']).
:- public(area/1).
:- mode(area(-integer), one).
:- info(area/1,
[comment is 'Rectangle area.',
argnames is ['Area']]).
:- public(move/3).
:- mode(move(+integer, +integer, -compound), one).
:- info(move/3, [
comment is 'Moves a rectangle to a new position, returning the updated rectangle.',
argnames is ['X', 'Y', 'NewRectangle']]).
:- public(position/2).
:- mode(position(?integer, ?integer), zero_or_one).
:- info(position/2, [
comment is 'Rectangle current position.',
argnames is ['X', 'Y']]).
init :-
parameter(1, 2), % Width
parameter(2, 1), % Height
parameter(3, 0), % X
parameter(4, 0). % Y
area(Area) :-
parameter(1, Width),
parameter(2, Height),
Area is Width*Height.
move(X, Y, rectangle(Width, Height, X, Y)) :-
parameter(1, Width),
parameter(2, Height).
position(X, Y) :-
parameter(3, X),
parameter(4, Y).
/* Alternative predicate definitions using this/1 instead of parameter/2
(see the User Manual for the pros and cons of both alternatives):
init :-
this(rectangle(2, 1, 0, 0)).
area(Area) :-
this(rectangle(Width, Height, _, _)),
Area is Width*Height.
move(X, Y, rectangle(Width, Height, X, Y)) :-
this(rectangle(Width, Height, _, _)).
position(X, Y) :-
this(rectangle(_, _, X, Y)).
*/
:- end_object.
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