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Re^3: $array[ 'Infinity' ]

by ikegami (Pope)
on Dec 16, 2007 at 23:38 UTC ( #657344=note: print w/replies, xml ) Need Help??

in reply to Re^2: $array[ 'Infinity' ]
in thread $array[ 'Infinity' ]

Is Perl suppose to support Infinity as a number? If so, it has two bugs: it doesn't work, and it's not in the docs. It's not in the 5.10.0 docs either.

It's not recognized by the parser:

>perl -e "use Devel::Peek; $x="Infinity"; Dump($x); $x=Infinity; Dump( +$x)" SV = PV(0x22612c) at 0x226000 REFCNT = 1 FLAGS = (POK,pPOK) PV = 0x182cb54 "Infinity"\0 CUR = 8 LEN = 12 SV = PV(0x22612c) at 0x226000 REFCNT = 1 FLAGS = (POK,pPOK) PV = 0x182cb54 "Infinity"\0 CUR = 8 LEN = 12 >perl -e "use Devel::Peek; $x="-Infinity"; Dump($x); $x=-Infinity; Dum +p($x)" SV = PV(0x226150) at 0x226000 REFCNT = 1 FLAGS = (POK,pPOK) PV = 0x1835404 "-Infinity"\0 CUR = 9 LEN = 12 SV = PV(0x226150) at 0x226000 REFCNT = 1 FLAGS = (POK,pPOK) PV = 0x1835404 "-Infinity"\0 CUR = 9 LEN = 12

I also get different output from the commands you issued.

>perl -le "print 0+(-Infinity)" 0 >perl -le "print 0+('Infinity')" 0
>perl -v This is perl, v5.8.8 built for MSWin32-x86-multi-thread (with 25 registered patches, see perl -V for more detail) Copyright 1987-2006, Larry Wall Binary build 817 [257965] provided by ActiveState http://www.ActiveSta Built Mar 20 2006 17:54:25 ...

Has this been discussed on P5P?

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Re^4: $array[ 'Infinity' ]
by ysth (Canon) on Dec 17, 2007 at 01:38 UTC
Re^4: $array[ 'Infinity' ]
by blokhead (Monsignor) on Dec 16, 2007 at 23:45 UTC
    I have no idea what it's supposed to do. I couldn't find anything in my local docs about it either (nor about NaN, which has similar behavior on my build).

    Maybe it depends on the local floating-point arithmetic library?

    Searching came up with: this perl5.porters msg, and also FMTYEWTK about is_numeric, which seems to suggest that perl calls to the atof() library function. Finally, bignum suggests that "Perl doesn't always handle bareword NaN/inf properly."


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[moritz]: I must say, when I was very active on perlmonks, I got really used to the markup and all the workflows
[moritz]: and then I didn't post for a while, and then tried to answer a question. It nearly drove me nuts
[moritz]: when you try to quote part of a question, you have to know/guess/reverse -engineer what kind of markup they used
[holli]: see? a/XpF4b
[moritz]: and stuff it into a <blockquote>...</ blockquote>, which is, like, not at all bulky
[moritz]: specially if you're used to markdown
[holli]: there probably is some nodelet hack that lets you use markdown :)
[LanX]: a) well ... you can use the xml-version to get the original code w/o need of reverse engineering
[moritz]: yes, and that's the next problem: there are piles of workarounds, but not solution, no visible progress
[LanX]: b) you cahnge my wikisyntax to support markdown and stay PM compatible

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