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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In reply to Re: Dangerous Names by ccn
in thread Dangerous Names by samtregar

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