Data.Time.Calendar.BankHoliday.EnglandAndWales

Calculation of bank holidays in England and Wales, using the rules that have been in place since 1978, and including all exceptions to the rules in the years 1995 to 2020. I do not know of any exceptions from 1978 until 1995, so the calculations may be correct for those years too. Calculations for future dates are predictions which may be rendered false if exceptions to the rules are announced.

There are normally 8 bank holidays in England and Wales:

• New Year's Day
• Good Friday
• Easter Monday
• May Day
• Spring Bank Holiday
• Summer Bank Holiday
• Christmas Day
• Boxing Day

The rules for determining the precise date of each of these in any given year are a little involved, since holidays may be moved to avoid falling on a weekend:

• The New Year's Day holiday is the 1st of January, or the following Monday if the 1st is a weekend.
• Good Friday and Easter Monday are the Friday and Monday either side of Easter Sunday (as calculated by the Gregorian method).
• May Day is the first Monday in May.
• The Spring Bank Holiday is the last Monday in May.
• The Summer Bank Holiday is the last Monday in August.
• Christmas Day is the 25th of December unless that's a weekend, in which case it's the 27th.
• Boxing Day is the 26th of December unless that's a weekend, in which case it's the 28th.

Exceptions may be made to these rules on a year-by-year basis.

This package is a reasonably efficient (constant-time) implementation of these rules.

Documentation

bankHolidays :: Integer -> [Day]

List the bank holidays for the given year, in ascending order. Bank holidays never fall on a weekend.

isBankHoliday :: Day -> Bool

Returns whether a day is a bank holiday.

countBankHolidays :: Day -> Day -> Integer

Count the number of bank holidays between two Days.

If d0 <= d1 then countBankHolidays d0 d1 is the number of Days d for which isBankHoliday d && d0 <= d && d < d1. Note the count includes d0 but excludes d1.

Additionally, countBankHolidays d0 d1 == negate (countBankHolidays d1 d0) and countBankHolidays d0 d2 == countBankHolidays d0 d1 + countBankHolidays d1 d2.