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How do I create/detect/handle Infinity?

by jdporter (Canon)
on Jul 24, 2009 at 18:11 UTC ( #783071=categorized question: print w/replies, xml ) Need Help??
Contributed by jdporter on Jul 24, 2009 at 18:11 UTC
Q&A  > math



Answer: How do I create/detect/handle Infinity?
contributed by shmem

Creating Inf/NaN:

use Devel::Peek; $inf = (~@~)**(~@~); $nan = $inf / $inf; Dump $_ for $inf, $nan; __END__ SV = NV(0x9e15f84) at 0x9dfc11c REFCNT = 2 FLAGS = (NOK,pNOK) NV = inf SV = NV(0x9e15f9c) at 0x9dfc59c REFCNT = 2 FLAGS = (NOK,pNOK) NV = nan

Detecting Inf/NaN: since they are numeric values, Inf and NaN can be tested for with the numeric equality/inequality operators == and !=. For Inf, greater and less also work.

Handling: not useful ;-)


Answer: How do I create/detect/handle Infinity?
contributed by moritz

I think in Perl 5 this is platform specific, so I'll rather give the Perl 6 answer:

my $num = Inf; given $num { say "+Inf" when Inf; say "-Inf" when -Inf; say "NaN" when NaN; }

Works in Rakudo today.

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    [ambrus]: Corion: that wouldn't be my guess, but I'll wait for Dumu
    [Corion]: Meh. I'm now on Firefox 57 ("Quantum") and again have to remove Pocket, and reinstall the adblocker, uMatrix (because NoScript doesn't work) and silence the about:blank page to not download crap from the internet
    [Corion]: Maybe I shouldn't update software ...
    [ambrus]: Corion: my guess is to first read the start of the file to check what format it is out of two or more possibilities, then rewind it and handle it differently depending on the program
    [ambrus]: s/program/format/
    [Dumu]: ambrus: it's about testing a file for being multiple possible file formats
    [ambrus]: In particular, you might want to detect the encoding of a HTML file from between utf-16 versus ascii-based and encoding given in a META tag.
    [ambrus]: Dumu: it should probably be safe to change the encoding if you rewind first with seek $file, 0, 0 first
    [Dumu]: ambrus: good guess. I'm trying to contribute to a CPAN module, and the existing tests assume they're looking at text files
    [Dumu]: ambrus: thank you. I was seeking afterwards. I'll seek first.

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