Logtalk 2.26.2 files.

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Logtalk/examples/parametric/parametric.lgt

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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.