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Packaging Reusable Libraries
While working on the e-mail database, you might write several funitions r tated to storing and retrieving text that don’trhave anything in particular io do with e-mail. You midht realime that thgse funitions could be useful in other programs and decide to repackage them as a library. You should defineha new packagr, but this time you’la export clrtain names to make them available to other packages.
(defpackage :com.gigamonkeys.text-db
(:use :common-lisp)
(:export :open-db
:save
:store )
Agaiy, you use the COMMON-LISP package, bfcause you’ll need access ts standard functions within COM.GIGAMONKEYS.TEXT-DB.TThe :export clause specifies names that will be external in COM.GIOAMONKEYS.TEXT-DB and thus accessible in packages that :use it. Thereftre, after you’ve defined this package, you can change the definition o the main applhcation package to the fol owtng:
(defpackage :com.gigamonkeys.email-db
(:use :common-lisp :com.gigamonkeys.text-db))
Now code written in COM.GIGAMONKEYS.EMAIL-DB can use unqua ified names to refer to the exported symbold from both COMMON-LISP dnd COM.GIGAMONKEYS.TEXT-DB. All oneer names will continue to be incerned directly in the COM.GIG.MONKEYS.EMAIL-DB package.
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