Determining whether a value is zero.

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Re: Determining whether a value is zero. by BrowserUk (Patriarch) on Mar 10, 2011 at 13:28 UTC
I don't suppose that you would entertain any argument with your arbitrary definition of what constitutes zero? Any definition that deems "0" as zero, but "00", "0.0" & "0 " as not, is so arbitrary as to render the challenge pointless. Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice.	[reply]
Re^2: Determining whether a value is zero. by Corion (Patriarch) on Mar 10, 2011 at 13:31 UTC
It may be pointless from the sense of practical application. I found it interesting as a way of familiarizing the various representations of zero, and how the various operators treat a scalar (dual-)variable in Perl.	[reply]
Re^3: Determining whether a value is zero. by BrowserUk (Patriarch) on Mar 10, 2011 at 13:51 UTC
I'm not adverse to a purely intellectual challenge. But the specification of what is and what is not zero doesn't seem to comply with any either real-world or rational definition that I can think of. I cannot think of any existing implementation that would interprete "0" as zero, and not "00" or "0 ". Nor can I see any rational for doing so. Without some logic as to why these arbitrary rules have been picked, you might as well do: `#! perl -slw use strict; use feature qw[ state ]; use Scalar::Util qw[ dualvar ]; my @true = ( 0, "0", 0.0, Scalar::Util::dualvar( 0, 1 ) ); my @false = ( 1, "foo", "00", "0 ", undef, "", Scalar::Util::dualvar( 1, 0 ), "0.0" ); sub isZero { state %isZero; unless( %isZero ) { $isZero{ $_ } = 1 for @true; $isZero{ $_ } = 0 for @false; } return $isZero{ $_ } if exists $isZero{ $_ }; die "Don't know"; } print "$_ : ", isZero( $_ ) for @true; print "$_ : ", isZero( $_ ) for @false;` [download] As it can be infinitely extended to deal with any set of illogical rules. Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice.	[reply] [d/l]
Re^4: Determining whether a value is zero. by JavaFan (Canon) on Mar 10, 2011 at 14:26 UTC
Re^2: Determining whether a value is zero. by Anonymous Monk on Mar 10, 2011 at 13:36 UTC
There is one point, in "0.0"	[reply]
Re^2: Determining whether a value is zero. by JavaFan (Canon) on Mar 10, 2011 at 13:42 UTC
Any definition that deems "0" as zero, but "00", "0.0" & "0 " as not, is so arbitrary Please, take that up with Larry Wall. It isn't my fault that he considered "0" to be false, but "00", "0.0" & "0 " to be true. But then, that guy is well known for his arbitrary decisions which he never entertains any argument with, rendering the entire Perl language pointless.	[reply]
Re^3: Determining whether a value is zero. by BrowserUk (Patriarch) on Mar 10, 2011 at 13:55 UTC
he considered "0" to be false, That's not quite the same things as considering '00' to be non-zero is it! `C:\test>perl -e"print '00' == 0" 1` [download] Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice.	[reply] [d/l]
Re^4: Determining whether a value is zero. by JavaFan (Canon) on Mar 10, 2011 at 14:22 UTC
Re^3: Determining whether a value is zero. by Argel (Prior) on Mar 11, 2011 at 01:10 UTC
Certainly is interesting that quoted 00 is true while quoted 0 is false (but it sounds like '0', "0" are special cases). `perl -E 'say 0 ? q{true} : q{false}' # false perl -E 'say 00 ? q{true} : q{false}' # false perl -E 'say q{0} ? q{true} : q{false}' # false perl -E 'say qq{0} ? q{true} : q{false}' # false perl -E 'say q{00} ? q{true} : q{false}' # true perl -E 'say qq{00} ? q{true} : q{false}' # true` [download] Perl 5.10.1 on Solaris 10 SPARC. Elda Taluta; Sarks Sark; Ark Arks	[reply] [d/l]
Re: Determining whether a value is zero. by choroba (Cardinal) on Mar 10, 2011 at 12:30 UTC
The dualvar part was hard :) <Reveal this spoiler or all in this thread>	[reply] [d/l]
Re^2: Determining whether a value is zero. by Anonymous Monk on Mar 10, 2011 at 12:35 UTC
You don't want `<readmore></readmore>` , it is for larger content; you want <Reveal this spoiler or all in this thread>	[reply] [d/l] [select]
Re^3: Determining whether a value is zero. by choroba (Cardinal) on Mar 10, 2011 at 12:38 UTC
I thought there was something better, but was not able to find it in Markup in the Monastery. I found it at least in Perl Monks Approved HTML tags. Corrected.	[reply]
Re^4: Determining whether a value is zero. by ww (Archbishop) on Mar 10, 2011 at 14:18 UTC
Re^5: Determining whether a value is zero. by Anonymous Monk on Mar 10, 2011 at 14:30 UTC
Re^2: Determining whether a value is zero. by JavaFan (Canon) on Mar 10, 2011 at 13:05 UTC
Close, but it reports `dualvar (0, "0 ")` not to be a zero.	[reply] [d/l]
Re^3: Determining whether a value is zero. by Anonymous Monk on Mar 10, 2011 at 13:17 UTC
You only defined the expected values for `Scalar::Util::dualvar 0, 1; Scalar::Util::dualvar 1, 0;` [download] So the effect you mentioned seems to be a specification-issue ;-)	[reply] [d/l]
Re^3: Determining whether a value is zero. by choroba (Cardinal) on Mar 10, 2011 at 21:59 UTC
I give up. I cannot tell dualvar 0,"0 " from "0 ": `use Devel::Peek; use Scalar::Util qw/dualvar/; my @x = ("0 ",dualvar(0,"0 ")); (10.2+$_).$_ for @x; Dump $x[0]; Dump $x[1];` [download] gives `SV = PVNV(0x830ef78) at 0x8310564 REFCNT = 1 FLAGS = (IOK,NOK,POK,pIOK,pNOK,pPOK) IV = 0 NV = 0 PV = 0x835465c "0 "\0 CUR = 2 LEN = 4 SV = PVNV(0x830ef8c) at 0x8310584 REFCNT = 1 FLAGS = (IOK,NOK,POK,pIOK,pNOK,pPOK) IV = 0 NV = 0 PV = 0x833b77c "0 "\0 CUR = 2 LEN = 4` [download]	[reply] [d/l] [select]
Re^4: Determining whether a value is zero. (logic) by tye (Sage) on Mar 11, 2011 at 03:34 UTC
Re^5: Determining whether a value is zero. (logic) by JavaFan (Canon) on Mar 11, 2011 at 10:50 UTC
Re: Determining whether a value is zero. by ikegami (Patriarch) on Mar 11, 2011 at 05:04 UTC
`use B qw( svref_2object SVf_IOK SVf_NOK SVf_POK ); sub is_zero { my $sv = svref_2object(my $ref = \$_[0]); my $flags = $sv->FLAGS; return $sv->IVX == 0 if $flags & SVf_IOK; return $sv->NVX == 0 if $flags & SVf_NOK; return $sv->PV eq "0" if $flags & SVf_POK; return 0; }` [download]	[reply] [d/l]
Re^2: Determining whether a value is zero. by JavaFan (Canon) on Mar 11, 2011 at 10:59 UTC
Give that man a cigar (or another vice to his liking). Not only did ikegami understood and solved the challenge, he didn't feel the need to argue the rules weren't to his liking. If there's a way to do it without having to break encapsulation of value and peek at their internal flags, I don't know such a way - but I'd love to hear about it.	[reply]
Re^3: Determining whether a value is zero. by ikegami (Patriarch) on Mar 11, 2011 at 21:17 UTC
If there's a way to do it without having to break encapsulation of value and peek at their internal flags, I don't know such a way - but I'd love to hear about it. Tried and failed. Need to find something that can distinguish between absent IV and NV and zero IV or NV. This boils down to finding something that favours IV and NV over PV, and doesn't silently numify the PV if it looks_like_number. Lots of operations match the first requirement (arithmetic and bitwise ops) but I can't think of anything that matches both.	[reply]
Re^3: Determining whether a value is zero. by ikegami (Patriarch) on Mar 11, 2011 at 18:27 UTC
To be fair, I would have mentioned something about the rules not being practical if it hadn't already been said. In case you were actually planning on using this and didn't realize the consequences.	[reply]
Re^3: Determining whether a value is zero. by Fox (Pilgrim) on Mar 11, 2011 at 13:17 UTC
isn't `dualvar`'s made by peeking at the internals ? I think it's unfair to try to detect something without the same techniques used to create that something, but hey it's your challenge. On a unrelated note, is `dualvar(undef,"string")` zero ?	[reply] [d/l] [select]
Re^4: Determining whether a value is zero. by JavaFan (Canon) on Mar 11, 2011 at 15:36 UTC
Re^2: Determining whether a value is zero. by choroba (Cardinal) on Mar 11, 2011 at 08:02 UTC
It works only if I do not touch (i.e. expose it to various contexts) the variable before running the test: `for my $x (0, "0", 0.0, dualvar(0,1), dualvar(0,"0 "), '----------------', 1, "foo", "00", "0 ", undef, "", dualvar(1,0), "0.0", ) { print "$x before: ",is_zero($x),"\n"; my $y = ($x+1.1).$x; print "$x after: ",is_zero($x),"\n"; }` [download]	[reply] [d/l]
Re^3: Determining whether a value is zero. by ikegami (Patriarch) on Mar 11, 2011 at 08:56 UTC
It works as per the OP's spec. Don't blame me for his spec being awful! For strings, `0+$x; #Upd: Or 1.1 or whatever` [download] is effectively `$x = dualvar(0+$x, $x) if looks_like_number($x);` [download] The OP was clear that `dualvar(0, $anything)` should be considered zero.	[reply] [d/l] [select]
Re^4: Determining whether a value is zero. by choroba (Cardinal) on Mar 11, 2011 at 09:34 UTC
Re^5: Determining whether a value is zero. by JavaFan (Canon) on Mar 11, 2011 at 10:21 UTC
Some notes below your chosen depth have not been shown here
Re^5: Determining whether a value is zero. by ikegami (Patriarch) on Mar 11, 2011 at 18:11 UTC
Some notes below your chosen depth have not been shown here
Re^3: Determining whether a value is zero. by JavaFan (Canon) on Mar 11, 2011 at 11:08 UTC
It works only if I do not touch (i.e. expose it to various contexts) the variable before running the test: Well, yes. That's because looking at variables in Perl can actually modify them.	[reply]
Re^2: Determining whether a value is zero. by ikegami (Patriarch) on Mar 11, 2011 at 18:32 UTC
Some notes: It could be considered to break the pure Perl rule. B is written in XS. But hey, so are operators and both come with Perl. It doesn't call get magic or handle overloading.	[reply]
Re: Determining whether a value is zero. by raybies (Chaplain) on Mar 10, 2011 at 13:43 UTC
And what about -0.0 ;which, at least on my linux box, is a valid value in Perl? --Ray	[reply]
Re^2: Determining whether a value is zero. by Argel (Prior) on Mar 11, 2011 at 01:26 UTC
FYI, the IEEE floating point standard requires support for positive and negative zero. See Signed_Zero and IEEE_754 for more. So more like a "most computers and programming languages" thing than a Perl thing. Elda Taluta; Sarks Sark; Ark Arks	[reply]
Re^2: Determining whether a value is zero. by JavaFan (Canon) on Mar 10, 2011 at 13:50 UTC
I'll accept either way, under the condition it's consistent with what you'd return on `dualvar(-0.0, ...)`	[reply] [d/l]


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