bignum incompatible with looks_like_number() ???

Apparently, "use bignum;" causes problems with looks_like_number.

Background:

My code makes a call to Finance::Math:IRR to compute an Internal Rate of
return.

my call looks like this:
$result = xirr(%HashOfDatesAndCashflows, precision => 0.000001);

This works fine, except that I'm getting answers that are a little off
numerically.

So, in my main .pl file, I added the line:
use bignum;

Which resulted in an error message:
ERROR: precision is not a valid number at /Users/cb/main.pl line 189

After digging around, I discovered that Finance::Math::IRR calls
looks_like_number($x) where $x is set to the value of the precision hash
key.

Sure enough, the debugger reveals that I'm calling xirr with:
         
'precision' => bless( {
                    '_m' => [1],
                        '_es' => '-',
                        '_e' => [6],
                        'sign' => '+'
                       }, 'Math::BigFloat' )

which SHOULD pass the looks_like_number test, but it doesn't.

I can't believe two such frequently-used components are incompatible.

bignyum is included in most Perl builds.

looks_like_number() is part of the perl api according to
http://search.cpan.org/~nwclark/perl-5.8.8/pod/perlapi.pod


What am I doing wrong?

I'm using Perl 5.8.6 under MacOS Darwin

Thanks
CB

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