Tricks of the Wizards

`Filter::Util::Call`

Here's a skeleton usage:

           package Rot13 ;

           use Filter::Util::Call ;

           sub import
           {
               my($type, @arguments) = @_ ;
               my $result = "";

               filter_add(
                   sub
                   {
                       my $status = filter_read() ;
                       if ($status >= 0) {
                         tr/A-Za-z/N-ZA-Mn-za-m/;
                       }
                       return $status;
                   } )
           }

1 ;

A filtering module should provide an import which calls filter_add
filter_add sets up the filter, which calls filter_read
filter_read places a line of code into $_
The filter modifies $_ and returns