root/tags/lgt2310/library/date.lgt

:- 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.