Day of the week: Difference between revisions

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 =={{header|GAP}}==
-<lang gap>xmas := function(a, b)
+<lang gap>Filtered([2008 .. 2121], y -> WeekDay([25, 12, y]) = "Sun");
+# [ 2011, 2016, 2022, 2033, 2039, 2044, 2050, 2061, 2067, 2072, 2078, 2089, 2095, 2101, 2107, 2112, 2118 ]
-  local y, v;
-  v := [ ];
+# A possible implementation of WeekDayAlt
-  for y in [a .. b] do
-    if WeekDay([25, 12, y]) = "Sun" then
+WeekDayAlt := function(args)
-      Add(v, y);
-    fi;
+   local d, m, y, k;
+   d := args[1];
-  od;
+   m := args[2];
-  return v;
+   y := args[3];
+   if m < 3 then
+      m := m + 12;
+      y := y - 1;
+   fi;
+   k := 1 + RemInt(d + QuoInt((m + 1)*26, 10) + y + QuoInt(y, 4)
+          + 6*QuoInt(y, 100) + QuoInt(y, 400) + 5, 7);
+   return days[k];
 end;
-xmas(2008, 2121);
+Filtered([2008 .. 2121], y -> WeekDayAlt([25, 12, y]) = "Sun");
 # [ 2011, 2016, 2022, 2033, 2039, 2044, 2050, 2061, 2067, 2072, 2078, 2089, 2095, 2101, 2107, 2112, 2118 ]</lang>