sub f {
#234567890#234567890#234567890#234567890#234567890#234567890
use Time::Local;(gmtime timegm 0,0,0,25,11,-1900+pop)[6]
}
[download]

_____________________________________________________
Jeff[japhy]Pinyan: Perl, regex, and perl hacker.
s++=END;++y(;-P)}y js++=;shajsj<++y(p-q)}?print:??;

55 ;-)

sub f {
    use Time'Local;(gmtime timegm 0,0,0,25,11,-1900+pop)[6]
}
[download]

--
John.

Except that you don't handle years before 1900. The problem-statement said that it handle to handle any year in the Common Era. :-)

------
We are the carpenters and bricklayers of the Information Age.

Don't go borrowing trouble. For programmers, this means Worry only about what you need to implement.

However, I would say two things about this. First using ' istead of :: is so ugly that it isn't worth the 1 stroke saving. Secondly, although Perl Golf involves bending the rules as much as possible, using modules just goes against the spirit of the game.

# 39
sub xmas1 {
    use Date'Manip;Date_DayOfWeek+12,25,pop
}

# 41
sub xmas2 {
    use Date'Calc':all';Day_of_Week+pop,12,25
}
[download]

# 37
sub xmas3 {
    use Date'Manip;Date_DayOfWeek+5,1,pop
}

# 39
sub xmas4 {
    use Date'Calc':all';Day_of_Week+pop,5,1
}
[download]

--
John.

sub f {
#234567890#234567890#234567890#234567890#234567890#
$b=1;$b+=1+!$_%4-!$_%100+!$_%400for(1..pop);$b%=7
}
[download]

sub f {
#234567890#234567890#234567890#234567890#234567890#23
$b=1;$b+=1+!($_%4)-!($_%100)+!($_%400)for 1..pop;$b%7
}
[download]

-----------------------------------------------------
Dr. Michael K. Neylon - mneylon-pm@masemware.com || "You've left the lens cap of your mind on again, Pinky" - The Brain
"I can see my house from here!"
It's not what you know, but knowing how to find it if you don't know that's important

Sorry, Masem. I trimmed it down to 47. Hey! 47!

sub f {
#234567890#234567890#234567890#234567890#234567890#
$b=1;$b+=1+!$_%4-!$_%100+!$_%400for 1..pop;$b%7
}
[download]

_____________________________________________________
Jeff[japhy]Pinyan: Perl, regex, and perl hacker.
s++=END;++y(;-P)}y js++=;shajsj<++y(p-q)}?print:??;

Unofficially, you shouldn't use modules in perl golf unless specifically called for or given as an option in the problem. (Hypothetically, you could write a module that does the bulk of the work though still be of utility to others outside of the golf, release it to CPAN, then use that module in your golf to crush the other players). Typically golfs with 70 or more characters will be benefitted by a module use, while for golfs less than that, the module might be more trouble (as you have to add 5 + lenght(module name) automatically to use the module.

-----------------------------------------------------
Dr. Michael K. Neylon - mneylon-pm@masemware.com || "You've left the lens cap of your mind on again, Pinky" - The Brain
"I can see my house from here!"
It's not what you know, but knowing how to find it if you don't know that's important

Are you guys using another version of perl than I am? At least here, the !-operator binds more tightly than the %-operator, so that (!$_%4 &c) just won't work.

... or am I just giving away your joke now ... ?

Anyway, I guess this would work (checking the calendar). 65 chars; based on yours:

sub f {
#234567890#234567890#234567890#234567890#234567890#234567890#234567890
+#234567890
for(1..($b=pop)++){$b++;$b--if$_%4;$b++if$_%100;$b--if$_%400}$b%7
}
[download]

sub f {
#234567890#234567890#234567890#234567890#234567890#2
$b+=$_%400?$_%100?$_%4?0:1:0:1for 1..($b=pop)++;$b%7
}
[download]

Update: Checking the calendar again ...

The Sidhekin
print "Just another Perl ${\(trickster and hacker)},"

This has a Golf Style Question attached to it...

Your answer can be trimmed down to 47 characters:

sub f {
  #23456789_123456789_123456789_123456789_123456789_12
  $b+=$_%400?$_%100?$_%4?1:2:1:2for 1..pop;$b%7+1
}
[download]

But this begs the question, should it be immediately reusable? My guess is yes, in which case this is a non-answer. The problem is that $b doesn't get reinitialized at the start of the sub so you have to either zero it or undef it in between every call.

It returns correctly the first time, but incorrectly after that; is this ok for a golf? Or should it return correctly every time?

jynx

jynx, your sub does not even return the correct answer the first time, if $b has been set elsewhere -- you rely on it to be numerically zero initially. Moreover, you will get a 7, not a 0, for Sundays ... so on the whole, I can't say I like it.

That is not to say my answer cannot be trimmed down. Indeed, I just did. And just so as not to leave your suggestion as the best (sorry; I really don't like it), I trimmed it to 46 chars:

sub f {
#        1         2         3         4         5
#234567890#234567890#234567890#234567890#234567890#23
$b+=!($_%4||/00$/&&$_%400)for 0..($b=pop);$b%7
}
[download]

Comparing that to my first suggestion ... can you tell I really like the ternary operator? ;-)

The Sidhekin
print "Just another Perl ${\(trickster and hacker)},"

sub f{
#234567890#234567890#234567890#234567890#234567890#234567890#23456
use Time'Piece;(Time'Piece->strptime("25Dec".pop,"%d%b%Y"))->_wday
}
[download]

-Blake