Re: shortest test for truth false assignment
On Wed, 22 May 2002, Scott Wiersdorf wrote:
What is the shortest way to test a variable for truth and then set its
value to false such that the truth test still succeeds?
if( $a ) {
$a = 0;
do_something();
}
I think you've got it. Since you specified the if-block structure as
fixed, and there has to be a reference to $a somewhere, there are only
five (5) non-whitespace strokes that could possibly be lost: $a=0;
If $a is mentioned twice, that leaves only three (3) strokes. That's
quite hard to beat. And I don't think there are any solutions short
enough that would only mention $a once, except for the clever Vi$a
trick. Unless $a is tied or something, which would be even further away
from the spirit of the challenge, I think.
Of course, there's this gem from the really-irresponsible-coding dept.:
*a = *|;
if ($a--) {
do_something();
}
Just make sure you don't select a different filehandle somewhere...
--
Ilmari Karonen - http://www.sci.fi/~iltzu/
I admit, the original poster didn't say they wanted a solution that was
good. They just said they wanted it to be multi-threaded.
-- Logan Shaw in comp.lang.perl.misc
Re: shortest test for truth false assignment
On Wed, 22 May 2002 13:04:53 -0600, Scott Wiersdorf wrote:
What is the shortest way to test a variable for truth and then set its
value to false such that the truth test still succeeds?
For example, I have a global variable $a (given) that is somehow set
to true. I want to test it for truth and do something:
snip
$a = 1;
...
if( $a ) {
$a = 0;
do_something();
}
Shortest? Huh... I don't care, personally. But I sometimes do this,
which has not too much redundancy (it only mentions $a once, for
example):
$a = do { do_something(); 0 };
$a will become 0 afterwards, the do BLOCK is only executed if $a was
true. That was what you asked for, isn't it?
--
Bart.
Re: shortest test for truth false assignment
hi,
what about:
$a($a=do_something0)
PM
http://marcell.hypermart.net/
Who cares what you think?
- Original Message -
From: Josh Goldberg [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Cc: [EMAIL PROTECTED]
Sent: Thursday, May 23, 2002 7:44 AM
Subject: RE: shortest test for truth false assignment
if($a){do_something($a=0)}
that's one stroke shorter
Re: shortest test for truth false assignment
I like - ($a =~ /$b/) ? do_something($a) : do_something($b); Unfortunately the shortest test may not be the right test. _Sx iudicium ferat: Perfer et obdura; dolor hic tibi proderit olim...
Re: shortest test for truth false assignment
how about
do_something($a=0) if $a;
On Wed, 22 May 2002, Scott Wiersdorf wrote:
My shortest try is this (10 characters w/o whitespace):
if( $a%2 .. $a-- ) {
do_something();
...
}
Re: shortest test for truth false assignment
On Wed, May 22, 2002 at 01:04:53PM -0600, Scott Wiersdorf wrote:
My shortest try is this (10 characters w/o whitespace):
if( $a%2 .. $a-- ) {
do_something();
...
}
I put the ellipses in there after the do_something() because there's
more to do after the do_something. It really is a block of statements
(though I don't care how they're executed, as long as it's done in
order). The ideas posted so far are excellent, but don't take the
blockish nature of this structure into account (of course, tmtowtdi).
Scott
--
Scott Wiersdorf
[EMAIL PROTECTED]
Re: shortest test for truth false assignment
On Wed, May 22, 2002 at 01:04:53PM -0600, Scott Wiersdorf wrote:
My shortest try is this (10 characters w/o whitespace):
if( $a%2 .. $a-- ) {
do_something();
...
}
Ok, this is also 10 characters:
if( $a=~s/.+// ) {
...
}
and has the (strange) benefit of only letting the empty string be
false (which is ok).
Scott
--
Scott Wiersdorf
[EMAIL PROTECTED]
RE: shortest test for truth false assignment
What about...
$a--do{do_something()};
If $a isn't 1, you could do this, too:
$a($a=0)||do{do_something()};
Right? I'm surprised noone's mentioned it, unless I'm missing something...
Patrick
Re: shortest test for truth false assignment
It looks like I missed the original message or something...but how about:
do_something(),do_something_else(),printwoohoo\n,etc,if$a%2..$a--;
It really depends on what you're doing, so this may not always work
depending on how it's all structured
-Samy
Scott Wiersdorf wrote:
On Wed, May 22, 2002 at 01:04:53PM -0600, Scott Wiersdorf wrote:
My shortest try is this (10 characters w/o whitespace):
if( $a%2 .. $a-- ) {
do_something();
...
}
I put the ellipses in there after the do_something() because there's
more to do after the do_something. It really is a block of statements
(though I don't care how they're executed, as long as it's done in
order). The ideas posted so far are excellent, but don't take the
blockish nature of this structure into account (of course, tmtowtdi).
Scott
--
Samy Kamkar -- cp5 -- [EMAIL PROTECTED]
LucidX.com / LA.pm.org / code.LucidX.com
Re: shortest test for truth false assignment
Quoting Scott Wiersdorf ([EMAIL PROTECTED]):
My shortest try is this (10 characters w/o whitespace):
if( $a%2 .. $a-- ) {
do_something();
...
}
I'm a little confused, but I'm assuming you're allowed to stipulate what the
true value is. In which case
if ($a$a--) {
do_something();
}
works, provided the true value is 1.
Adam
--
Adam Rice -- [EMAIL PROTECTED] -- Blackburn, Lancashire, England
Re: shortest test for truth false assignment
On Wed, May 22, 2002 at 03:36:06PM -0400, Patrick Gaskill wrote:
What about...
$a--do{do_something()};
If $a isn't 1, you could do this, too:
$a($a=0)||do{do_something()};
Right? I'm surprised noone's mentioned it, unless I'm missing something...
These statements unconditionally alter $a (unless _I'm_ missing
something). $a should only be set to 0/false iff $a is 1/true.
Scott
--
Scott Wiersdorf
[EMAIL PROTECTED]
Re: shortest test for truth false assignment
Quoting Scott Wiersdorf ([EMAIL PROTECTED]):
if( $a%2 .. $a-- ) {
do_something();
...
}
I think my favourite is
if (Vi$a) {
do_something();
}
Adam
PS. Of course, you have to do something like
sub Vi { if ($_[0]) { $_[0]=0; return 1; } else { return 0; } }
somewhere else in your program, but that's a small price to pay for a
splendid obfuscation.
--
Adam Rice -- [EMAIL PROTECTED] -- Blackburn, Lancashire, England
RE: shortest test for truth false assignment
heh or better still $a$a--do_something; :) -Original Message- From: disciple [mailto:[EMAIL PROTECTED]] Sent: 22 May 2002 21:35 To: [EMAIL PROTECTED] Subject: RE: shortest test for truth false assignment The more obscure looking the better... $a$a--do_something();
RE: shortest test for truth false assignment
Scott writes: What is the shortest way to test a variable for truth and then set its value to false such that the truth test still succeeds? Hmmm .. so, after the test, no matter what the inital value of your variable is, it will be false. So: $ado_something();$a=0; --Ala
RE: shortest test for truth false assignment
On Wed, 22 May 2002, Patrick Gaskill wrote: Ah, but did you try running this? $a-- will be false, meaning it will short-circuit, and never get to do_something(). I think you are confusing $a$a--do_something(); with $a--$ado_something(); -- Philippe BRUHAT - BooK Financez le développement de Perl, avec YAS et les Mongueurs de Perl ! http://www.mongueurs.net/association/actions/pdg2002.html
Re: shortest test for truth false assignment
Scott Wiersdorf:
if( $a%2 .. $a-- ) {
I don't understand this. You see, if $a-- leaves $a as false, then:
if ($a--)
is the shortest way of solving the problem. And if not, then your
code above won't work:
% perl -le '$a=2;if( $a%2 .. $a-- ) {print Hi}; print $a'
2
(2 is, you will note, a true value)
But sticking to the spirit of the game:
% perl -le '$a=2; if ($a..($a=0)) { print Hi }; print $a'
Hi
0
--
About the use of language: it is impossible to sharpen a pencil with a blunt
ax. It is equally vain to try to do it with ten blunt axes instead.
-- Edsger Dijkstra
Re: shortest test for truth false assignment
On Wed, May 22, 2002 at 10:45:39PM +0100, Simon Cozens wrote:
Scott Wiersdorf:
if( $a%2 .. $a-- ) {
I don't understand this. You see, if $a-- leaves $a as false, then:
if ($a--)
is the shortest way of solving the problem.
But that will change $a to true if it was false.
Here's what I understand the goal to be:
If $a is true, set $a to false and execute some code
If $a is false, do nothing.
Ronald
Re: shortest test for truth false assignment
On Wed, May 22, 2002 at 10:55:52PM +0100, Simon Cozens wrote:
Ronald J Kimball:
if( $a%2 .. $a-- ) {
Here's what I understand the goal to be:
If $a is true, set $a to false and execute some code
But the code above doesn't do that for all true values.
Sorry, I left out a condition. You can choose what values to use for true
and false. (As implied in the original message, It doesn't have to be
numeric (i.e., bit strings or any true/false values will work).)
Ronald
RE: shortest test for truth false assignment
Scot et al,
Just a point if clarification. The code we're supposed to golf must be
funcationally equivalent to:
if( $a ) {
$a = 0;
do_something();
}
## and now $a is false
Where were we told the do_something couldn't mess with $a? In which case
Ala's solution
$ado_something();$a=0
is the only one so far that works for all do_something()'s
Scot. Is $a guaranteed to be untouched?
Alistair
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Re: shortest test for truth false assignment
On Wed, May 22, 2002 at 11:11:13PM +0100, [EMAIL PROTECTED]
wrote:
Scot. Is $a guaranteed to be untouched?
Perhaps some context would help (and possibly present alternative
solutions, though these have been really fun).
Imagine something like this:
## $a is a flag that indicates we should do something
$SIG{HUP} = sub { $a++ };
while( 1 ) {
foo();
...
bar();
...
## check to see if we need to reread config file
if( data_is_stale() || $a ) {
$a = 0;
reread_config_file();
do_something_else();
do_yet_something_else();
}
## now $a is 0 and the above code won't get invoked again until
## someone sends us a HUP
}
For simplicity's sake, I reduced the problem to what Alistair quoted
above:
if( $a ) {
$a = 0;
do_something();
do_something_else();
...
}
Hence my original question: can the 'if( $a ) { $a = 0; ... }'
construct be done in fewer characters than my best try:
if( $a%2 .. $a-- ) {
do_something();
...
}
My example assumes the following constraints: $a is zero (or any even
number) to begin with. This next example doesn't assume digits, but it
does require the starting value of $a to be the empty string:
$SIG{HUP} = sub { $a='foo' };
$a = '';
while( 1 ) {
yada_yada();
if( $a=~s/.*// ) {
do_something();
...
}
}
I don't care what constraints you impose, as long as the block gets
executed exactly once and only when $a is true (for whatever you want
to define as true).
Shortest (looking) answer yet (which several people posted) is:
$a $a-- do {
do_something();
...
}
Two questions: a) can it be shortened to fewer characters? and b) is
there another way to do it better in general?
This has been a fun thread, btw (for me, anyway). Thanks.
Scott
--
Scott Wiersdorf
[EMAIL PROTECTED]
Re: shortest test for truth false assignment
In article [EMAIL PROTECTED],
Scott Wiersdorf [EMAIL PROTECTED] wrote:
$a $a-- do {
do_something();
...
}
Two questions: a) can it be shortened to fewer characters? and b) is
there another way to do it better in general?
This is longer (not to mention demented) but should work with any true value:
(($a)=$a?():$a)|| do { ... }
Re: shortest test for truth false assignment
On Wed, May 22, 2002 at 10:06:39PM -0400, Josh Goldberg wrote:
I came up with another one. This also works for values of true other
than 1.
if ($a=~tr/.[^0]+/0/c) { do_something(); }
s/tr/s/, maybe ?
(the transliterate operator doesn't use patterns, so
the code above change every instances of '.' by a 0,
of '[' by a '[' and so on and so forth...)
Joy,
`/anick
--
On the whole, human beings want to be good,
but not too good, and not quite all the time.
-- George Orwell
Re: shortest test for truth false assignment
If tr doesn't use patterns then please help me understand how it works
in my test cases?
btw a straight swap to s/// fails for true == 1 but works for true ==
'foo'.
#!/usr/bin/perl
for (1,'foo',0) {
$a = $_;
test();
test();
}
sub test {
print $a ;
if ($a=~tr/.[^0]+/0/cs) { do_something(); }
print $a\n;
}
sub do_something {
print - ;
}
output:
1 - 0
0 0
foo - 0
0 0
On Wed, 22 May 2002, Yanick wrote:
On Wed, May 22, 2002 at 10:06:39PM -0400, Josh Goldberg wrote:
I came up with another one. This also works for values of true other
than 1.
if ($a=~tr/.[^0]+/0/c) { do_something(); }
s/tr/s/, maybe ?
(the transliterate operator doesn't use patterns, so
the code above change every instances of '.' by a 0,
of '[' by a '[' and so on and so forth...)
Joy,
`/anick
--
On the whole, human beings want to be good,
but not too good, and not quite all the time.
-- George Orwell
Re: shortest test for truth false assignment
On Wed, May 22, 2002 at 09:54:52PM -0400, Yanick wrote:
On Wed, May 22, 2002 at 10:06:39PM -0400, Josh Goldberg wrote:
I came up with another one. This also works for values of true other
than 1.
if ($a=~tr/.[^0]+/0/c) { do_something(); }
s/tr/s/, maybe ?
(the transliterate operator doesn't use patterns, so
the code above change every instances of '.' by a 0,
of '[' by a '[' and so on and so forth...)
Actually, it translates every character that is *not* one of '.[^0]+' into '0'.
/c complements the search list.
When the search list is longer than the replacement list, the last
character in the replacement class is repeated.
Ronald
Re: shortest test for truth false assignment
ahhh, I get it now, thanks.
On Wed, 22 May 2002, Ronald J Kimball wrote:
On Wed, May 22, 2002 at 09:54:52PM -0400, Yanick wrote:
On Wed, May 22, 2002 at 10:06:39PM -0400, Josh Goldberg wrote:
I came up with another one. This also works for values of true other
than 1.
if ($a=~tr/.[^0]+/0/c) { do_something(); }
s/tr/s/, maybe ?
(the transliterate operator doesn't use patterns, so
the code above change every instances of '.' by a 0,
of '[' by a '[' and so on and so forth...)
Actually, it translates every character that is *not* one of '.[^0]+' into '0'.
/c complements the search list.
When the search list is longer than the replacement list, the last
character in the replacement class is repeated.
Ronald
Re: shortest test for truth false assignment
so then
if($a=~tr/0/0/c) {do_something();}
should work for any value of true, right?
On Wed, 22 May 2002, Ronald J Kimball wrote:
On Wed, May 22, 2002 at 09:54:52PM -0400, Yanick wrote:
On Wed, May 22, 2002 at 10:06:39PM -0400, Josh Goldberg wrote:
I came up with another one. This also works for values of true other
than 1.
if ($a=~tr/.[^0]+/0/c) { do_something(); }
s/tr/s/, maybe ?
(the transliterate operator doesn't use patterns, so
the code above change every instances of '.' by a 0,
of '[' by a '[' and so on and so forth...)
Actually, it translates every character that is *not* one of '.[^0]+' into '0'.
/c complements the search list.
When the search list is longer than the replacement list, the last
character in the replacement class is repeated.
Ronald
Re: shortest test for truth false assignment
In article [EMAIL PROTECTED],
Ronald J Kimball [EMAIL PROTECTED] wrote:
if ($a=~tr/.[^0]+/0/c) { do_something(); }
Actually, it translates every character that is *not* one of '.[^0]+' into '0'.
Which means it does work, with slightly altered true/false semantics
than are usual for perl. (true means contains non-^,+,],[,.,0
character(s)).
Even the simplified:
if ($a=~y/0/0/c) { ... }
has e.g. 00 as false when by usual perl semantics it is true.
You could just as well say:
if ($a=~y/x/x/c) { ... }
and have true mean contains non-x characters, false mean empty or only x's.
RE: shortest test for truth false assignment
Sorry, I just realised even that won't work as in modifies the state
regardless.
-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
Sent: Thursday, 23 May 2002 12:36
To: [EMAIL PROTECTED]
Subject: RE: shortest test for truth false assignment
Scott,
I don't believe that you'll be able to shorten:
if($a){$a=0;do_something()}
any further unless you're able to use the flip-flop instead of $a:
if($|--){do_something()}
All suggestions so far have been longer.
hth
ty
-Original Message-
From: Scott Wiersdorf [mailto:[EMAIL PROTECTED]]
Sent: Thursday, 23 May 2002 05:05
To: [EMAIL PROTECTED]
Subject: shortest test for truth false assignment
Hello fwp'ers,
Here's a golfish problem that I thought some people might enjoy:
What is the shortest way to test a variable for truth and
then set its
value to false such that the truth test still succeeds?
For example, I have a global variable $a (given) that is somehow set
to true. I want to test it for truth and do something:
snip
$a = 1;
...
if( $a ) {
$a = 0;
do_something();
}
## and now $a is false
...
/snip
You can't do this:
if( $a = $a ? 0 : $a ) {
do_something();
...
}
because the whole expression becomes false when $a is assigned 0.
My shortest try is this (10 characters w/o whitespace):
if( $a%2 .. $a-- ) {
do_something();
...
}
Assuming warnings and stricture, can anyone find a shorter
test/assignment? It doesn't have to be numeric (i.e., bit strings or
any true/false values will work).
Good luck!
Scott
--
Scott Wiersdorf
[EMAIL PROTECTED]
RE: shortest test for truth false assignment
if($a){do_something($a=0)}
that's one stroke shorter
On Thu, 23 May 2002 [EMAIL PROTECTED] wrote:
I don't believe that you'll be able to shorten:
if($a){$a=0;do_something()}
any further unless you're able to use the flip-flop instead of $a:
if($|--){do_something()}
All suggestions so far have been longer.
