Holiday Specification

Class: Holiday

Package: com.waysysweb.util

Author: W. Shaffer

Date: 11-Nov-2006

Description:

This structure handles holiday calculations.

See http://en.wikipedia.org/wiki/Federal_holidays#List_of_Holidays

See also http://www.opm.gov/fedhol/2006.asp

See also http://aa.usno.navy.mil/faq/docs/easter.html

Maintenance:

Date Author Description

----------- ------ -----------------------------------------------------------

11-Nov-2006 Shaffer File created

structure HOLIDAY = struct

(*============ Exceptions ==============================================*)

(*============ Imports =============================================*)

(* Date imports *)

type WayDate = WAYDATE.WayDate;

type Month = WAYDATE.Month;

type Day = WAYDATE.Day;

type Year = WAYDATE.Year;

type DayOfYear = WAYDATE.DayOfYear;

type DayOfWeek = WAYDATE.DayOfWeek;

fun add(date1 : WayDate, value : int) : WayDate =

WAYDATE.add(date1, value);

fun numDayOfWeek(dayOfWeek : DayOfWeek) : int =

WAYDATE.numDayOfWeek(dayOfWeek);

fun dayOfWeek(date1 : WayDate) : DayOfWeek =

WAYDATE.dayOfWeek(date1);

fun daysInMonth(mnth : Month, yr : Year) : Day =

WAYDATE.daysInMonth(mnth, yr);

(* Date set *)

type DateSet = DATERANGE.DateSet;

fun max(set : DateSet, pred : WayDate -> bool) : WayDate =

DATERANGE.max(set, pred);

fun range(fromDate : WayDate, thruDate : WayDate) : DateSet =

DATERANGE.range(fromDate, thruDate);

(*============ Types =============================================*)

(* Day Positions *)

datatype DayPosition = First | Second | Third | Fourth | Last;

(*============ Constants ==============================================*)

(*============ Properties ==============================================*)

(*============ Attributes =============================================*)

(*============ Invariant =============================================*)

(*============ Initialization ==========================================*)

fun create(mnth : Month, dy : Day, yr : Year) : WayDate =

WAYDATE.create(mnth, dy, yr);

(*============ Operations =============================================*)

(* ------------ Date positioning functions ----------------------------- *)

(* Day of week on or before *)

fun dayOfWeekOnOrBefore(date : WayDate, dyOfWk : DayOfWeek) : WayDate =

let

val datePriorWeek = add(date, ~6);

val dateRange = range(datePriorWeek, date);

fun pred(adate : WayDate) : bool = dayOfWeek(adate) = dyOfWk

max(dateRange, pred)

end;

(* Day of week on or after *)

fun dayOfWeekAfter(date1 : WayDate, dyOfWk : DayOfWeek) : WayDate =

dayOfWeekOnOrBefore(add(date1, 7), dyOfWk);

(* Day of week after *)

fun dayOfWeekBefore(date1 : WayDate, dyOfWk : DayOfWeek) : WayDate =

dayOfWeekOnOrBefore(add(date1, ~1), dyOfWk);

(* Nth Day from Date *)

fun nthDayFromDate( First, dyOfWk : DayOfWeek, date1 : WayDate) : WayDate =

add(dayOfWeekBefore(date1, dyOfWk), 7)

| nthDayFromDate( Second, dyOfWk : DayOfWeek, date1 : WayDate) : WayDate =

add(dayOfWeekBefore(date1, dyOfWk), 14)

| nthDayFromDate( Third, dyOfWk : DayOfWeek, date1 : WayDate) : WayDate =

add(dayOfWeekBefore(date1, dyOfWk), 21)

| nthDayFromDate( Fourth, dyOfWk : DayOfWeek, date1 : WayDate) : WayDate =

add(dayOfWeekBefore(date1, dyOfWk), 28)

| nthDayFromDate( Last, dyOfWk : DayOfWeek, date1 : WayDate) : WayDate =

add(dayOfWeekAfter (date1, dyOfWk), ~7);

(* Date from position *)

fun dateFromPosition( mnth : Month, Last, dow : DayOfWeek, yr : Year) =

nthDayFromDate(Last, dow, create(mnth, daysInMonth(mnth, yr), yr))

| dateFromPosition( mnth : Month, dy : DayPosition, dow : DayOfWeek, yr : Year) =

nthDayFromDate(dy, dow, create(mnth, 1, yr));

(* Observed holiday *)

fun calcObservedHoliday(date : WayDate) : WayDate =

case dayOfWeek(date) of

WAYDATE.Saturday => WAYDATE.decrement(date)

| WAYDATE.Sunday => WAYDATE.increment(date)

| _ => date;

(* ------------ Supporting routines for Easter calculation ------------- *)

(* century - determine the century from a year *)

fun century(yr : Year) : int = (yr div 100) + 1;

fun shiftedEpact(yr : Year) : int =

let

val cent = century(yr)

(14 + (11 * (yr mod 19)) - ((3 * cent) div 4) + ((5 + 8 * cent) div 25))

mod 30

end;

fun adjustedEpact(yr : Year) : int =

let

val shifted = shiftedEpact(yr)

if shifted = 0 orelse ( (shifted = 1) andalso (10 < (yr mod 19)))

then shifted + 1

else shifted

end;

fun paschalMoon(yr : Year) : WayDate =

let

val paschal = adjustedEpact(yr)

add(create(4, 19, yr), ~ (paschal))

end;

(* ------------ US Federal Holidays ------------------------------------ *)

(* New Year's Day *)

fun NewYearsDay(yr : Year) : WayDate =

create(1, 1, yr);

(* Birthday of Martin Luther King, Jr. *)

fun MartinLutherKingsBirthday(yr : Year) : WayDate =

dateFromPosition(1, Third, WAYDATE.Monday, yr);

(* Washington's Birthday *)

fun WashingtonsBirthday(yr : Year) : WayDate =

dateFromPosition(2, Third, WAYDATE.Monday, yr);

(* Memorial Day *)

fun MemorialDay(yr : Year) : WayDate =

dateFromPosition(5, Last, WAYDATE.Monday, yr);

(* Independence Day *)

fun IndependenceDay(yr : Year) : WayDate =

create(7, 4, yr);

(* Labor Day *)

fun LaborDay(yr : Year) : WayDate =

dateFromPosition(9,First, WAYDATE.Monday, yr);

(* Columbus Day *)

fun ColumbusDay(yr : Year) : WayDate =

dateFromPosition(10, Second, WAYDATE.Monday, yr);

(* Veteran's Day *)

fun VeteransDay(yr : Year) : WayDate =

create(11, 11, yr);

(* Thanksgiving *)

fun ThanksgivingDay(yr : Year) : WayDate =

dateFromPosition(11, Fourth, WAYDATE.Thursday, yr);

(* Christmas *)

fun Christmas(yr : Year) : WayDate =

create(12, 25, yr);

(* ------------ Easter ------------------------------------------------- *)

(* Easter *)

fun Easter(yr : Year) : WayDate =

dayOfWeekAfter(paschalMoon(yr), WAYDATE.Sunday);

end (* HOLIDAY *)