Doomsday rule: Difference between revisions
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02/12/2077: Friday
04/02/2101: Saturday</pre>
=={{header|jq}}==
{{trans|Julia}}
{{works with|jq}}
'''Works with gojq, the Go implementation of jq'''
Note that the assertions as defined here are only checked if the environment variable JQ_ASSERT is set.
<lang jq>
def weekdaynames: ["Sunday", "Monday","Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"];
# For months 1 through 12, the date of the first doomsday that month.
def leapyear_firstdoomsdays: [4, 1, 7, 4, 2, 6, 4, 1, 5, 3, 7, 5];
def nonleapyear_firstdoomsdays: [3, 7, 7, 4, 2, 6, 4, 1, 5, 3, 7, 5];
# get_weekday(year::Int; month::Int; day::Int)::String
# Return the weekday of a given date in the past or future subject to 1582<=$year<=9999.
# Uses Conway's doomsday rule (see also https://en.wikipedia.org/wiki/Doomsday_rule)
def assert(exp; msg):
if env.JQ_ASSERT then
(exp as $e | if $e then . else . as $in | "assertion violation: \(msg) => \($e)" | error end)
else . end;
def get_weekday($year; $month; $day):
# sanity checks
assert(1582 <= $year and $year <= 9999; "Invalid year (\($year) - should be after 1581 and 4 digits)")
| assert( 1 <= $month and $month <= 12; "Invalid month, should be between 1 and 12")
| assert( 1 <= $day and $day <= 31; "Invalid day, should be between 1 and 31")
# Conway's doomsday algorithm
| ((2 + 5 * ($year % 4) + 4 * ($year % 100) + 6 * ($year % 400)) % 7) as $doomsday
# leap year determination:
| (if (($year % 4 != 0) or ($year % 100 == 0 and $year % 400 != 0))
then nonleapyear_firstdoomsdays[$month - 1]
else leapyear_firstdoomsdays[$month - 1]
end) as $anchorday
| (($doomsday + $day - $anchorday + 7) % 7) as $weekday # IO==0
| weekdaynames[$weekday] ;
("January 6, 1800 was on a " + get_weekday(1800; 1; 6)),
("March 29, 1875 was on a " + get_weekday(1875; 3; 29)),
("December 7, 1915 was on a " + get_weekday(1915; 12; 7)),
("December 23, 1970 was on a " + get_weekday(1970; 12; 23)),
("May 14, 2043 will be on a " + get_weekday(2043; 5; 14)),
("February 12, 2077 will be on a "+ get_weekday(2077; 2; 12)),
("April 2, 2101 will be on a " + get_weekday(2101; 4; 2)),
("April 2, 21011 will be on a " + get_weekday(21011; 4; 2))</lang>
{{out}}
<pre>
January 6, 1800 was on a Monday
March 29, 1875 was on a Monday
December 7, 1915 was on a Tuesday
December 23, 1970 was on a Wednesday
May 14, 2043 will be on a Thursday
February 12, 2077 will be on a Friday
April 2, 2101 will be on a Saturday
April 2, 21011 will be on a Tuesday
</pre>
=={{header|Julia}}==
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