Weren't there a whole pile of warnings about using source filters at one point?
The Switch module mistakenly escaped into Perl 5.8.
Do not use it.
The Switch module was deprecated in Perl 5.10 and removed in Perl 5.14.
Notice that in Categorized Damian Modules, the Switch module is categorized
by its author as
"Damian modules you shouldn't use in production because
their purpose is to explore and prototype future core language features".