This was discussed in the thread spawned by node "Ensuring forward compatibility". In summary, the answer is that if you mention the keyword 'package' then the interpreter knows you're talking in perl5.

So consider package main; to be equivalent to use perl5;. And, of course, all your existing modules already have a package so will Just Work <cough><splutter>.

In reply to Re^3: Perl 6 critique is a good thing by DrHyde
in thread Perl 6 critique is a good thing by Juerd

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