Merry Golfmas, Everyone!

Question

It's Christmas everybody, and here's a code-golf challenge to celebrate. You need to make a program to print out a present. Specifically, the words "Merry Christmas". BUT, there is a catch: this program must only work if it is the 25th of December. If the code is run on any other day, then the program should crash.

This is Code-Golf, so the answer with the least amount of bytes wins.

Merry Christmas!

Answer 1

Pyke, 21 bytes

.dↄґ6C65h*325q/Al

Try it here!

     C65h*        -   multiply the day by the (current month + 1)
          325q    -  ^ == 325
    6         /   - 6 / ^
.dↄґ              -  load "merry christmas"
               Al - ^.capwords()

Or 18 bytes noncompetitive.

.dↄґ6Cs6Y1q/Al

Exactly the same except for this section:

Cs6Y1q 
C      -    get_time()
 s6    -   add 1 week
   Y   -  get day of the year
    1q - ^ == 1

Try it here!

Answer 2

JavaScript, 55 53 46 bytes

^{Note: this has only been tested in Google Chrome, program may behave differently from browser to browser (or device to device)}

2 bytes saved thanks to @ConorO'Brien

7 bytes saved thanks to @ETHProductions

alert(/c 25/.test(Date())?"Merry Christmas":a)

Exits with Uncaught ReferenceError: a is not defined if the date is not Dec 25. I'm not really sure if this counts as crashing

alert(/c 25/.test(Date())?"Merry Christmas":a)

Answer 3

Python 3, 66 63 bytes

Thanks to ideas from JavaScript / ES answers here I managed to squeeze some bytes. Index a dictionary - non-existent keys will raise a KeyError. The following code works in local time zone

import time;print({1:'Merry Christmas'}['c 25'in time.ctime()])

The output format for ctime isn't locale-dependent - the format is always ~ 'Sun Dec 25 19:23:05 2016'. Since only in December does the 3-letter abbreviation end with c, it is safe to use 'c 25'in time.ctime() here.

---

Previous version:

This works in UTC time zone. For local time zone one needs to s/gm/local for 3 more bytes. For Python 2, one can remove parentheses from print for 65 bytes.

import time;print({(12,25):'Merry Christmas'}[time.gmtime()[1:3]])

The construct throws KeyError on other dates:

>>> import time;print({(1,1):'Happy New Year'}[time.gmtime()[1:3]])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: (12, 25)

Answer 4

PHP, 39 38 bytes, not competing (doesn´t crash)

<?=date(md)-1225?"":"Merry Christmas";

or

<?date(md)-1225?die:0?>Merry Christmas

or

<?=["Merry Christmas"][date(md)-1225];

Answer 5

Python 2, 68 67 65 bytes

-1 with thanks to @muddyfish

Thanks to @AnttiHaapala for the idea that saved another couple.

import time;print['Merry Christmas'][(12,25)!=time.gmtime()[1:3]]

Try it online!

Throws an IndexError if not 25th Dec.

Non-competing version for 59 bytes as it only works for non Leap years (uses day of year which is 360 this year but 361 in leap years)

import time;print['Merry Christmas'][360!=time.gmtime()[7]]

Answer 6

R, 52 61 58 bytes

`if`(format(Sys.Date(),"%m%d")=="1225","Merry Christmas",)

If the current date is not the 25th of December then an error is returned because no third argument is supplied to if.

Edit: Fixed a silly error

Answer 7

My first time around here... Started with the best language ever for this job:

Java, 200 188 bytes (thanks to @Daniel Gray), 186 bytes removing "ln" from print.

import java.util.*;public class a{public static void main(String[]r){Calendar c=Calendar.getInstance();if(!(c.get(2)==11&&c.get(5)==25)){int i=1/0;}System.out.print("Merry Christmas");}}

Try it here!

Answer 8

MATL, 34 33 bytes

'Merry Christmas'IHh&Z'5U12h=?}Yl

This works in current version (19.7.0) of the language. To cause the error, the following code exploits the fact that the logarithm of a string gives an error (this may change in future versions).

Try it online!

Explanation

'Merry Christmas'  % Push this string
IHh                % Push 3, then 2, concatenate: gives array [3 2]
&Z'                % Get 3rd and 2nd outputs of clock vector: current day and month
5U12h              % Push 5, square, push 12, concatenate: gives [25 12]
=                  % Compare if corresponding entries are equal in the two arrays
?                  % If all entries are equal: do nothing
}                  % Else
  Yl               %   Logarithm. Gives an error when applied on a string
                   % End (implicit). Display (implicit)

Answer 9

QBIC, 48 bytes

~left$$|(_D,5)=@12-25||?@Merry Christmas|\?a(12)

Explanation:

~             IF
left$$|(_D,5) the date string starts with
=@12-25|      the string "12-25"
|             THEN
[email protected]|     PRINT "Merry Christmas"
\             ELSE
?a(12)        Print the twelfth index of an undefined array. 
              Since there are only 11 elements in undefined arrays, this 
              results in an index-out-of-bounds error.    
The the IF statement is auto-closed by QBIC.

This assumes American MM-DD date notation. This would be shorter if I'd finally make a Substring function in QBIC.

Answer 10

05AB1E, 32 21 bytes

Saved 11 bytes thanks to Adnan's string compression :) .

1žfže‚12D·>‚Q÷”ÞٌΔ×

Explanation

 žfže‚                Push [current month, current day]
      12D·>‚          Push [12, 25]
            Q         Push tmp = 1 if the two arrays are equal, tmp = 0 otherwise
1            ÷        Evaluate x = 1/tmp. If tmp = 0 a division by 0 exception is thrown
              ”ÞÙŒÎ”× Implicitly display "Merry Christmas" x times

Try it online!

I did what came to mind first, so there may be better approaches for this one. But PPCG deserves a Merry Christmas in 05AB1E as well ;) .

Answer 11

C# / CS Script 106 100 99 bytes

99 byte solution

using System;int i;Console.WriteLine(DateTime.Now.ToString("dM")=="2512"?"Merry Christmas":i/0+"");

Try it here!

100 byte solution (prefer this one... a bit different)

using System;int i;Console.WriteLine(DateTime.Now.AddDays(7).DayOfYear==1?"Merry Christmas":i/0+"");

Explained:

using System;
int i;

// if today plus 7 days is the first day of the year, then it's xmas!
Console.WriteLine(DateTime.Now.AddDays(7).DayOfYear==1
    ? "Merry Christmas"

// otherwise divide i by 0
    : i/0+"");

DateTime.Now.AddDays(7).DayOfYear==1 is one byte shorter than DateTime.Now.ToString("ddMM")=="2512" but 1 byte longer than DateTime.Now.ToString("dM")=="2512"

Answer 12

C#/CS Script, 96 Bytes, Mostly Plagiarized from Erresen

using System;Console.WriteLine(DateTime.Now.AddDays(7).DayOfYear==1?"Merry Christmas":1/0+"");

Deletes the int i declaration in favor of hard coding the division. I would leave this as a comment but don't have the reputation.

Answer 13

bash + Unix utilities, 51 49 47 bytes

((`date +%m%d`-1225))&&${};echo Merry Christmas

*Thanks to @KenY-N for pointing out that the quotes in the echo can be removed, and to @IporSircer for reducing the condition size by 2 bytes.

Answer 14

Groovy, 57 bytes

print new Date().format("Md")=="1225"?"Merry Christmas":b

Crashes on dates other than 25.12. with groovy.lang.MissingPropertyException because b is not defined.

Answer 15

Stacked, 42 bytes

Try it here!

('Merry Christmas')'MMDD'date'1225'=¬#out

This creates a single-element array containing namely 'Merry Christmas!'. After, it puts the date into a string with the month followed by the day. It checks for equality with '1225' (Christmas), inverts it with ¬, then gets that member from the preceding array. If it isn't Christmas, this will error with an index error. Otherwise, it prints Merry Christmas. (Change the date in the string to see how it works on other days.)

Answer 16

Batch, 66 bytes

@echo off
if %date:~0,5%==25/12 echo Merry Christmas&exit/b
if

The trailing newline is significant, as it causes parsing of the if statement to fail. You may need to tweak the date check to match your local date format.

Answer 17

Python 2, 69 77 75 or 72 70 Bytes

import time
if time.strftime("%d%m")=="2512":print"Merry Christmas"
else:1/0

If it doesn't matter if it exits with an error when it is Christmas, then:

import time
if time.strftime("%d%m")=="2512":print"Merry Christmas"
1/0

EDIT:

Thanks @Flp.Tkc for pointing out that I needed to raise an error

-2 Bytes from @Max for pointing out about removing colons from the strftime function

Answer 18

CJam, 28

et[C25]#1="Merry Christmas"/

Try it online

Explanation:

et                   push an array of current [year month day hour ...]
[C25]                push the array [12 25] (C=12)
#                    find the position of the 2nd array within the first one
1=                   compare it with 1, resulting in 1 for 1 and 0 otherwise
"Merry Christmas"/   split "Merry Christmas" into pieces of that length
                      (it crashes if the length is 0)
                     at the end, all the pieces are concatenated
                      and printed automatically

Answer 19

C#.NET, 180 172 171 bytes

Saved 8 bytes thanks to Kritixi Lithos

Saved 1 byte thanks to Kritixi Lithos, again ;)

namespace System{class P{static void Main(string[] args){var d=DateTime.Today;if(d.Day==25)if(d.Month>11){Console.Write("Merry Christmas!");return;}throw new Exception();}}}

Alternative, ungolfed variant:

namespace System //In System, so we don't have to use system.
{
    class Program
    {
        static void Main(string[] args) //Main function.
        {
            var d = DateTime.Today; //Get Today.
            if (d.Day == 25) if (d.Month == 12) //Day has to be 25th, Month has to be 12nd.
                {
                    Console.Write("Merry Christmas!"); return; //Prints.
                }
            throw new NotChristmasException(); //Errors/Crashes the program.
        }
    }
    class NotChristmasException : Exception { } //Holiday exception, hooray!
}

Answer 20

Mathematica, 46 bytes

If[Today[[1,2;;]]=={12,25},"Merry Christmas!"]

Answer 21

Common Lisp, 140

(let((m(multiple-value-list(decode-universal-time(get-universal-time)))))(if(and(eq(nth 3 m)25)(eq(nth 4 m)12))(write"Merry Christmas")(c)))

Crashes with undefined function if the date isn't right.

Answer 22

awk, 29 bytes (+ length("Merry xmas"))

v=1225==strftime("%m%d")||1/0

Running it:

$ echo Merry xmas | awk 'v=1225==strftime("%m%d")||1/0'
awk: cmd. line:1: (FILENAME=- FNR=1) fatal: division by zero attempted

Season greeting is piped to awk. strftime returns month+day (for example 1226) and if it matches 1225 $0 record gets outputed. Result of comparison 1225==1226 is placed to v var which is used to divide 1 if the date comparison fails.

Answer 23

Haskell, 116

Crashes with "Non-exhaustive patterns in function f" if it's not Christmas.

import Data.Time
f(_,12,25)="Merry Christmas"
main=getZonedTime>>=print.f.toGregorian.localDay.zonedTimeToLocalTime

Unfortunately, there's no function that allows you to just immediately get the time in a useful format, so most of this is converting the date formats.

Answer 24

C#, 122 104 bytes

18 bytes saved, thanks to @raznagul

using System;i=>{if(DateTime.Now.AddDays(7).DayOfYear==1)Console.Write("Merry Christmas");else{i/=0;};};

It adds 7 days to the current day, and checks if it is the first day of the year, if yes, it displays "Merry Christmas", otherwise it divides by zero.

Answer 25

Ruby, 69 bytes

if Time.now.strftime("%j")=="360";puts "Merry Christmas";else 0/0;end

Works in 2016. Doesn't differentiate between normal and leap years, may need to be adjusted for non-leap years.

Answer 26

ForceLang, 180 bytes

set s datetime.toDateString datetime.now()
set t "Dec 25"
def c s.charAt i
def d t.charAt i
set i -1
label 1
set i 1+i
if i=6
 io.write "Merry Christmas!"
 exit()
if c=d
goto 1
z.z

(Remember that datetime.toDateString is locale-dependent, so this may not work depending on your locale)

Answer 27

C#, 90 bytes

using System;Console.Write(new[]{"Merry Christmas"}[DateTime.Now.AddDays(7).DayOfYear-1]);

Throws IndexOutOfRangeException if it's not christmas.

Try it here!

Answer 28

bash command line, 45 48 49 48 bytes

date +%m%d|grep -q 1225&&echo Merry Christmas||!-
date +%m%d|grep -q 1225||!-;echo Merry Christmas

Similar to Mitchell Spector's, but use grep in silent mode to check for a match, then && will ensure that it only prints on success, and the || causes it to look up history with !-, which gives me this:

-bash: !-: event not found

And it stops execution as !- ; echo foo demonstrates. The bash documentation says that !-n refers to the current command minus n, so perhaps it is being interpreted as !-0, which gives an identical (and non-localised) error message.