unless (open (QTREES, $file))  {
    print STDERR "WARNING: get_qtrees() can't open $file for filer $filer!\n";
    return;
};

##</code><code>##

open (QTREES, $file) or {
    print STDERR "WARNING: get_qtrees() can't open $file for filer $filer!\n";
    return;
};

##</code><code>##

syntax error at ~chayashida/Perl/Module.pm line 872, near "return"
Global symbol "$filer" requires explicit package name at ~chayashida/Perl/Module.pm line 880.