Just for the heck of it, I'd thought I'd throw out the perl5 version...

$oporm = qr{[+-]?};
$digit = qr{\d};
$fixed = qr{  $oporm $digit+ \.? $digit* 
            | $oporm $digit* \.? $digit+ }x;

$scino = qr{  $fixed [eE] $oporm $digit+ | $fixed | $digit+ }x;

sub is_scino 
{
    my $num = shift;
    if ($num =~ m/^$scino$/)
    {
        $num = $num + 0;  # is this really necessary?
        return $num;
    }
        return undef;
}

sub is_fixed 
{
    my $num = shift;
    if ($num =~ m/^$fixed$/)
    {
        $num = $num + 0;
        return $num;
     }
     return undef;
}
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