in reply to Re^2: Controlling "use" statements
in thread Controlling "use" statements

use CGI::Carp qw(fatalsToBrowser set_message)

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is a shortcut for 

BEGIN {
   require CGI::Carp;
   import  CGI::Carp qw(fatalsToBrowser set_message);
}

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You can easily add an if in there. 

BEGIN {
   if ($DEBUG) {
      require CGI::Carp;
      import  CGI::Carp qw(fatalsToBrowser set_message);
   }
}

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In Section Seekers of Perl Wisdom