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:- object(date,
implements(datep)).
:- info([
version is 1.1,
author is 'Paulo Moura',
date is 2006/3/7,
comment is 'Date predicates.']).
today(Year, Month, Day) :-
{'$lgt_current_date'(Year, Month, Day)}.
leap_year(Year) :-
( 0 =:= mod(Year, 4), 0 =\= mod(Year, 100) ->
true
; 0 =:= mod(Year, 400)
).
name_of_day(1, 'Sunday', 'Sun').
name_of_day(2, 'Monday', 'Mon').
name_of_day(3, 'Tuesday', 'Tue').
name_of_day(4, 'Wednesday', 'Wed').
name_of_day(5, 'Thursday', 'Thu').
name_of_day(6, 'Friday', 'Fri').
name_of_day(7, 'Saturday', 'Sat').
name_of_month( 1, 'January', 'Jan').
name_of_month( 2, 'February', 'Feb').
name_of_month( 3, 'March', 'Mar').
name_of_month( 4, 'April', 'Apr').
name_of_month( 5, 'May', 'May').
name_of_month( 6, 'June', 'Jun').
name_of_month( 7, 'July', 'Jul').
name_of_month( 8, 'August', 'Aug').
name_of_month( 9, 'September', 'Sep').
name_of_month(10, 'October', 'Oct').
name_of_month(11, 'November', 'Nov').
name_of_month(12, 'December', 'Dec').
days_in_month( 1, _, 31).
days_in_month( 2, Year, Days) :-
leap_year(Year) -> Days = 29; Days = 28.
days_in_month( 3, _, 31).
days_in_month( 4, _, 30).
days_in_month( 5, _, 31).
days_in_month( 6, _, 30).
days_in_month( 7, _, 31).
days_in_month( 8, _, 31).
days_in_month( 9, _, 30).
days_in_month(10, _, 31).
days_in_month(11, _, 30).
days_in_month(12, _, 31).
valid(Year, Month, Day) :-
integer(Year),
integer(Month), Month >= 1, Month =< 12,
integer(Day),
days_in_month(Month, Year, Days),
Day >= 1, Day =< Days.
:- end_object.
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