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B.24. Embedding

The reverse of dynamic loading (in a sense) is embedding.

Suppose you want to make a really cool word processor, and you start writing it in (say) C++.[420] Now, you decide you want the users to be able to use Perl's regular expressions for an extra-powerful search-and-replace feature, so you embed Perl into your program. Then you realize that you could open up some of the power of Perl to your users. A power user could write a subroutine in Perl that could become a menu item in your program. Users can customize the operation of your word processor by writing a little Perl. Now you open up a little space on your website where users can share and exchange these Perl snippets, and you've got thousands of new programmers extending what your program can do at no extra cost to your company. And how much do you have to pay Larry for all this? Nothing -- see the licenses that come with Perl. Larry is a really nice guy. You should at least send him a thank-you note.

[420]That's probably the language we'd use for writing a word processor. Hey, we love Perl, but we didn't swear an oath in blood to use no other language. When language X is the best choice, use language X. But often, X equals Perl.

Although we don't know of such a word processor, some folks have already used this technique to make other powerful programs. One such example is Apache's mod_perl, which embeds Perl into an already-powerful web server. If you're thinking about embedding Perl, you should check out mod_perl; since it's all open source, you can see just how it works.



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