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]
... or my best, so far, at 52: 
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)},"

In reply to Re: Golfing the day of Christmas by Sidhekin
in thread Christmas Coding Blues by cacharbe

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