Technically, you can do all of the same things with just pure Perl that you can do with all of the modules on CPAN installed. For that matter, technically, you could do all of the same stuff with C or assembly language, or anything else that's Turing-equivalent. (If you're not familiar with this concept, do a Google Groups search for Turing Equivalence.)

So, why do we have CPAN then? Because in practice there's often a big difference between technically can be done and what it is suitably convenient or worthwhile to do. It is *possible* to write an email client in pure Perl with no modules, but it will take you weeks just to get a very basic working start. With POP3Client, Net::DNS, and Net::SMTP, you can have the same amount done in hours. It is *possible* to write database stuff in pure Perl to interface with an RDBMS, but with DBI you can do it in a *lot* less time. It is *possible* to study up on PKWare's Zip archive file format and write your own Perl code to read and write zipfiles, but you'll spend days or weeks; with Archive::Zip you can do it in an afternoon and have time left over for testing.

In short, the value of CPAN is not in what it enables you to do, but in what it saves you from needing to do.

$;=sub{$/};@;=map{my($a,$b)=($_,$;);$;=sub{$a.$b->()}}
split//,".rekcah lreP rehtona tsuJ";$\=$ ;->();print$/
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