Isnumber function

Can anyone explain this to me, it returns 1 when a number is passed and 0 if a non number is passed to it, but I don't understand how.

sub isNumber {
my $n = shift;
local $noError = 1;
local $^W = 1;
local $SIG{__WARN__} = sub { $noError = undef };
eval { my $x = $n + 0 };
return ($noError);
}

Hi!

Everything happens in this line:
eval { my $x = $n + 0 };

The sub is testing whether a number (i.e. 0) may be added to the input without causing a warn. If this succeeds, the input is a number. Otherwise it's text, etc.
The remaining parts of the sub is just overhead to assign the input, define some vars and to redirect the warn.

Regards,

Atrus.