my $have_SWE;
BEGIN {
  $have_SWE = 0;
  eval { require Spreadsheet::WriteExcel };
  unless ($@) {
     Spreadsheet::WriteExcel->import();
     $have_SWE = 1;
  }
}
if ($have_SWE == 1) { ... }


##</code><code>##

my $have_Tk;
BEGIN {
  $have_Tk = 0;
  eval { require Tk };
  $have_Tk = 1 unless ($@);
}
if ($have_Tk == 1) { ... }