From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-0.8 required=5.0 tests=BAYES_00,INVALID_DATE autolearn=no autolearn_force=no version=3.4.4 Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!watmath!clyde!caip!nike!ucbcad!ucbvax!SEI.CMU.EDU!Stefan.Landherr From: Stefan.Landherr@SEI.CMU.EDU Newsgroups: net.lang.ada Subject: package CALENDAR and time zones Message-ID: <8606262126.AA21565@bs.sei.cmu.edu> Date: Thu, 26-Jun-86 17:26:13 EDT Article-I.D.: bs.8606262126.AA21565 Posted: Thu Jun 26 17:26:13 1986 Date-Received: Sun, 29-Jun-86 05:32:51 EDT Sender: daemon@ucbvax.BERKELEY.EDU Organization: The ARPA Internet List-Id: Reference: R.G. Cleaveland @DCA-EMS 25-Jun-86 17:28(?) --------- I agree that the CALENDAR package is deficient in not catering for world time zones. However most users are interested in local time only, so any extension of CALENDAR and any interim solution should be transparent to such users. In addition, a calendar package with time zones should : (1) be useful all over the world (no parochialism), (2) cater for those places on half-hour time zones (eg South Australia), (3) have access to the current local time zone, (5) allow an (alterable) default zone for interpretation of times, (4) allow conversions between time zones, and (5) allow arithmetic and comparisons between times in different zones. To actually designate the time zones, I recommend the usual system of letters: Z for GMT A, B, C, D, E, F, G, H, I, K, L, M for hours ahead of GMT N, O, P, Q, R, S, T, U, V, W, X, Y for hours behind GMT two-letter combinations (eg IK) for half-hour zones ------------------------------------------------------------------------------ My suggestion for the long-term solution (i.e. for Ada 88) is: ------------------------------------------------------------------------------ package CALENDAR is type TIME is private; -- includes the time zone subtype YEAR_NUMBER is ..... ... -- unchanged subtype DAY_DURATION is .... type TIME_ZONE is (Y,YX,X,XW,W, .. ,N,NZ,Z,ZA,A,AB, .. ,L,LM,M); -- half hour time zones forward from International Dateline function LOCAL_TIME_ZONE return TIME_ZONE; -- from operating system DEFAULT_ZONE : TIME_ZONE := LOCAL_TIME_ZONE; function CLOCK return TIME; function YEAR (DATE : TIME; ZONE : TIME_ZONE := DEFAULT_ZONE) return YEAR_NUMBER; function MONTH ... return MONTH_NUMBER; -- function DAY ... return DAY_NUMBER; -- like YEAR function SECONDS ... return DAY_DURATION; -- procedure SPLIT (DATE : in TIME; YEAR ... MONTH ... DAY ... SECONDS ... ZONE : in TIME_ZONE := DEFAULT_ZONE) function TIME_OF (YEAR ... MONTH ... DAY ... SECONDS ... ZONE : in TIME_ZONE := DEFAULT_ZONE) return TIME; function "+" ... ... -- unchanged function ">=" ... TIME_ERROR ... -- unchanged private -- implementation dependent end CALENDAR; ------------------------------------------------------------------------------ In theory, implementations would be free to use any time zone for the internal representation of TIME values, and the time zone returned by function CLOCK is immaterial, provided that the TIME value is in fact the correct world-time. However, for portability, all Ada TIME values are best stored in GMT. Access to LOCAL_TIME_ZONE is required for portability of programs that input or output years, months, days etc. Conversion between time zones is through the ZONE parameter. A function to extract the time zone of a TIME value is not needed, (and could be abused). If DEFAULT_ZONE is left unchanged, then the use of time zones is quite transparent to "local-time-only" users. ------------------------------------------------------------------------------ For convenience, parochial acronyms for civil time zones can be introduced by additional, normal packages: eg with CALENDAR; use CALENDAR; package USA_TIME_ZONES is type USA_TIME_ZONE is (PST, PDT, MST, MDT, CST, CDT, EST, EDT); -- order not significant type CIVIL_TIME_MODE is (STANDARD, DAYLIGHT); function USA_TIME_ZONE (WORLD_ZONE : TIME_ZONE MODE : CIVIL_TIME_MODE ) return USA_TIME_ZONE; function PST return TIME_ZONE; -- returns U function PDT return TIME_ZONE; -- returns T function MST return TIME_ZONE; -- returns T function MDT return TIME_ZONE; -- returns S function CST return TIME_ZONE; -- returns S function CDT return TIME_ZONE; -- returns R function EST return TIME_ZONE; -- returns R function EDT return TIME_ZONE; -- returns Q ERROR : exception; -- raised by USA_TIME_ZONE for illegal inputs end USA_TIME_ZONES; ------------------------------------------------------------------------------ As an interim solution, I suggest that the enhanced CALENDAR package be provided as an additional pre-defined package under a different name (eg WORLD_CALENDAR) for use by those who need it. ------------------------------------------------------------------------------ It could be argued that package CALENDAR is also deficient in not providing facilities for: (1) time of day (both 12 hour and 24-hour clock) (2) names of months (abbreviated and in full) (3) names of days of week (abbreviated and in full) (4) correct day of week for any given date etc However none of these require unusual interaction with the operating system, and thus need not be part of a predefined package, but can be provided as normal packages. Stefan F. Landherr