:- object(date(_Year, _Month, _Day)).
:- info([
version is 1.0,
author is 'Paulo Moura',
date is 1998/3/23,
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)},
parameter(1, Year),
parameter(2, Month),
leap_year :-
(0 is mod(Year, 4),
0 is mod(Year, 100)
;
0 is mod(Year, 400)),
!.
:- end_object.
