in reply to Dangerous Names

Perl wants to see numbers around <=> (spaceship) operator and converts strings to numbers. "Nan" and "NaN" are both converted to zero.

Update: Strings which start with "nan" (/^nan/i) are converted to nan, others which start with "inf" (/^inf/i) converted to inf. Others are converted to zero unless begin with digits.

see perldoc peldata (Scalar values) 

#!/usr/bin/perl -l --
use strict;
use warnings;

my @s =qw(nan naNo inf InfInity infimum foo bar 123dd);
print "$_ => ", $_+0 for @s;

__END__

Argument "naNo" isn't numeric in addition (+) at a.pl line 7.
Argument "infimum" isn't numeric in addition (+) at a.pl line 7.
Argument "foo" isn't numeric in addition (+) at a.pl line 7.
Argument "bar" isn't numeric in addition (+) at a.pl line 7.
Argument "123dd" isn't numeric in addition (+) at a.pl line 7.
nan => nan
naNo => nan
inf => inf
InfInity => inf
infimum => inf
foo => 0
bar => 0
123dd => 123

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Re^2: Dangerous Names
by samtregar (Abbot) on Dec 17, 2008 at 21:58 UTC
    Incorrect! Proof: 

    $ perl -e '@names = (["Nan Tregar"], ["Sam Tregar"]); @names = sort { 
+$a->[0] <=> $b->[0] } @names;'
Sort subroutine didn't return a numeric value at -e line 1.

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    Note that you have to work a little. Just a straight { $a <=> $b } gets optimized into something that doesn't do the NaN conversion.

    -sam

[reply]
[d/l]
      I didn't need to do any extra work. See my post below. 
      $ perl -v
This is perl, v5.8.8 built for x86_64-linux-gnu-thread-multi

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[reply]
[d/l]
        Ok - but do you find it unusual that sort { $a <=> $b } doesn't die, but sort { $a->[0] <=> $b->[0] } does?

        -sam

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