A Date.T is a moment in time, expressed according to the standard (Gregorian) calendar, as observed in some time zone. A Date.TimeZone (or just a time zone) is an object that encapsulates the rules for converting from UTC (universal coordinated time, sometimes known as Greenwich mean time) to local time within a particular jurisdiction, taking into account daylight time when appropriate. \index{calendar date} \index{local time} \index{time!local} \index{time zone} \index{time!zone} \index{universal coordinated time} \index{time!UTC (universal coordinated time)} \index{Greenwich mean time} \index{time!Greenwich mean time} \index{time!Date interface@{\tt Date} interface}

INTERFACE Date;

IMPORT Time;

TYPE
  T = RECORD
    year: CARDINAL; (* e.g., 1992 *)
    month: Month;
    day: [1 .. 31];
    hour: [0 .. 23];
    minute: [0 .. 59];
    second: [0 .. 60];
    offset: INTEGER;
    zone: TEXT;
    weekDay: WeekDay
  END;
  Month = {Jan, Feb, Mar, Apr, May, Jun, Jul,
            Aug, Sep, Oct, Nov, Dec};
  WeekDay = {Sun, Mon, Tue, Wed, Thu, Fri, Sat};

TYPE TimeZone <: REFANY;

VAR Local, UTC: TimeZone;

Local is initialized to the time zone in which the computer running this program is located. UTC is initialized to the time zone for universal coordinated time.

PROCEDURE FromTime(t: Time.T; z: TimeZone := NIL): T;

Return the date corresponding to t, as observed in the time zone z. If z is NIL, Local is used.

EXCEPTION Error;

PROCEDURE ToTime(READONLY d: T): Time.T RAISES {Error};

Return the time corresponding to the date d, using the field offset rather than zone and ignoring the field weekDay. Raise Error if d cannot be represented as a Time.T.

END Date.