We had a question once which only failed on Sundays

Question

Inspired by We had a unit test once which only failed on Sundays, write a program or function that does nothing but throw an error when it is Sunday, and exit gracefully on any other day.

Rules:

• No using input or showing output through the usual IO methods, except to print to STDERR or your language's equivalent. You are allowed to print to STDOUT if it's a by-product of your error.
• A function may return a value on non-Sundays as long as it doesn't print anything
• Your program may use a Sunday from any timezone, or the local timezone, as long as it is consistent.
• An error is a something that makes the program terminate abnormally, such as a divide by zero error or using an uninitialised variable. This means that if any code were to be added after the part that errors, it would not be executed on Sunday.
• You can also use statements that manually create an error, equivalent to Python’s raise.
• This includes runtime errors, syntax errors and errors while compiling (good luck with that!)
• On an error there must be some sign that distinguishes it from having no error
• This is code-golf, so the shortest bytecount in each language wins!

I'll have to wait til Sunday to check the answers ;)

Answer 1

Groovy, 16 bytes

1/new Date().day

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Answer 2

Zsh, 15 bytes

${(%):-%(w._.)}

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Prompt sequences can be really crazy sometimes...

${(%):-%(w._.)}
${(%)         }   # expand as prompt sequence
     :-           # ${var:-fallback}, but without the var
       %( . .)    # Prompt ternary
         w        # If DoW matches given number (implied 0, which is Sunday)
          ._      # Then substitute _
            .     # Else substitute nothing

Since _ is not a command, it fails on Sunday.

Answer 3

R, 40 bytes

stopifnot(weekdays(Sys.Date(),T)!="Sun")

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weekdays returns the weekday of the date, with an optional argument abbreviate, which shortens Sunday to Sun, saving a single byte.

stopifnot throws an error if, for each argument, not all are TRUE, and throws an error with a message indicating the first element of which isn't TRUE, so the error is Error: "Sun" is not TRUE

Answer 4

Gema, 40 characters

\A=@subst{Su=\@err\{S\}\;*=;@datime}@end

Had to specify an error message, so choose a short one: “S”.

Sample run:

bash-4.4$ faketime 2018-01-06 gema '\A=@subst{Su=\@err\{S\}\;*=;@datime}@end'

bash-4.4$ faketime 2018-01-07 gema '\A=@subst{Su=\@err\{S\}\;*=;@datime}@end'
S

Answer 5

Funky, 21 bytes

if!os.date"%w"error()

os.date"%w" returns the current day of the week in 0-6 format, where 0 is sunday. Getting the logical not of that is only true when the weekday is 0, so Sunday. Then just a basic if(a){error()} will assure that this program only errors on sunday

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Answer 6

Perl 6,  29  21 bytes

die if now.Date.day-of-week>6

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die if now/86400%7+^3

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Answer 7

Pure bash BASH (interactive mode + no coreutils required), 17 20 19 bytes

PS1='`((1/\D{%w}))&&:`'

Now only 19 bytes thanks to manatwork's comment below.

Bonus, if you put it in your bashrc it fails every sunday you log in :-) not just when you run it on sundays!

Answer 8

Excel, 77 30 bytes

Yes, vastly more golfable.

=IF(WEEKDAY(TODAY())=1,1/0,"")

Simply checks if it's Sunday, and if so, finds the quickest way I know of to error. If not Sunday, returns "",the closest Excel has to not returning anything

Answer 9

C# (.NET Core), 39 43 41 bytes

_=>{if(1/(int)DateTime.Now.DayOfWeek<0);}

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Thanks to @caird coinheringaahing and @Jo King

Answer 10

Postgresql, 32

Not sure if you need to add ; at the end for valid answer

SELECT 1/EXTRACT(DOW FROM now())

Answer 11

SmileBASIC, 20 bytes

DTREAD OUT,,,W
W=W/W

DTREAD outputs the current year, month, day, and day of the week. Sunday is 0.

Answer 12

Java 8, 34 bytes

Returns 1 on Mondays, 0 on other days, and throws an ArithmeticException on Sundays

v->1/new java.util.Date().getDay()

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Answer 13

05AB1E, 54 52 bytes

žg¦¦D4÷že+•YFóåι•žf<è+žg4Öžf3‹&-ŽPjžg2£4%è++7%iõEëõ}

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Explanation

Formula from here.

žg¦¦                                                 # Take the last two digits of the year.
    D                                                # Save for later.
     4÷                                              # Divide by 4, discarding any fraction.
       že+                                           # Add the day of the month.
          •YFóåι•                                    # Push the month's key values.
                 žf                                  # Take the month.
                   <è                                # Find the month's key value.
                     +                               # Add the month's key value.
                      žg4Ö                           # Is this year a leap year?
                          žf3‹                       # Is it January or Feburary?
                              &                      # And the results of both questions.
                               -                     # Subtract 1 for January or February of a leap year.
                                ŽPj                  # Push 6420.
                                   žg2£              # Take the first two digits of the year.
                                       4%è           # Index the thing into the list.
                                          +          # Do step 6.
                                           +         # Add the last two digits of the year.
                                            7%       # Divide by 7 and take the remainder.
                                              i  ë } # Sunday is 1, so it goes in the if.
                                              iõ ë } # Push empty string.
                                              i Eë } # For loop.
                                              i  ëõ} # If not sunday, push empty string and implicit output.

Answer 14

Pyth, 7 bytes

/1-6.d9

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/1-6.d9
    .d9  // Current day of the week, 0 indexed on monday.
  -6     // 6 - day of week (0 if Sunday)
/1       // 1 ÷ ^

Answer 15

Japt, 7 bytes

çKe ªUí

Test it

çKe ªUí
ç           :U=0 times repeat
 K          :  Current date
  e         :  0-based day of the week
    ª       :  Logical OR with
     Uí     :  The result of running the í method on U, which doesn't exist for numbers

Answer 16

Python 3, 50 bytes

from datetime import*
1/(date.today().weekday()-6)

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Answer 17

Batch, 88 bytes

@for /f "skip=1" %%d in ('wmic path win32_localtime get dayofweek')do @set/a1/%%d&exit/b

Tries to divide by zero on Sunday.

Unfortunately neither date nor powershell date work on my PC to give me the day of the week.

Answer 18

PowerShell, 24 20 Bytes

1/(date).DayOfWeek>1

Sunday triggers divide by zero same as most of the other solution here. Problem is that on other days that a double gets returned so redirect to nowhere useful trumps that output.

Answer 19

Swift 4, 78 bytes

import Foundation;if(Calendar.current.component(.day,from:Date()))==7{exit(1)}

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Answer 20

AWK, 27 25 23 21 bytes

END{1/strftime("%w")}

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Saved 4 bytes thanks to manatwork

Saved 2 bytes thanks to mik

Answer 21

Octave, 23 22 bytes

(1:6)(weekday(now)-1);

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This will try to access an element in 1:6. When the day is Sunday it will try to access the element (1-1)=(0) which will result in an error as MATLAB is 1-indexed.

---

Original for 23.

assert(weekday(now)~=1)

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assert(...) will throw an error when the condition is false. weekday(now) returns the current day of the week where 1 = Sunday. Put the two together, the code will throw an error only on sundays when the condition becomes 1~=1.

Answer 22

Clojure, 43 bytes

#(and(=(.getDay(java.util.Date.))7)(/ 1 0))

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Uses the fact that and doesn't evaluate the second argument unless necessary. I originally thought I could get away with using the Ratio literal 1/0 to save two bytes, but that unfortunately causes exceptions immediately. It must try to reduce the Ratio right away or something.

(defn sunday-fail []
  (and (= (.getDay (Date.)) 7)
       (/ 1 0)))