Initial data commit

Task/Doomsday-rule/Factor/doomsday-rule.factor

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+USING: accessors calendar calendar.english formatting
+generalizations kernel math math.order math.vectors sequences ;
+
+: check-year ( year -- )  ! months and days checked by <date>
+    1582 9999 between?
+    [ "Year must be between 1582 and 9999." throw ] unless ;
+
+: doomsday ( year -- n )
+    { 4 100 400 } [ mod ] with map { 5 4 6 } vdot 2 + 7 mod ;
+
+: anchorday ( year month -- m )
+    1 - swap leap-year? { 4 1 } { 3 7 } ?
+    { 7 4 2 6 4 1 5 3 7 5 } append nth ;
+
+: weekday ( date -- str )
+    [ year>> dup check-year doomsday ] [ day>> + ]
+    [ dup year>> swap month>> anchorday - 7 + 7 mod ] tri
+    day-names nth ;
+
+: test ( date -- )
+    [ "%B %d, %Y" strftime ]
+    [ now before? "was" "will be" ? ]
+    [ weekday ] tri
+    "%s %s on a %s.\n" printf ;
+
+1800 1 6
+1875 3 29
+1915 12 7
+1970 12 23
+2043 5 14
+2077 2 12
+2101 4 2
+[ <date> test ] 3 7 mnapply