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2.4.2 Relative Package Names ¶

Relative package names are needed for the same reason as relative pathnames, for brevity and to reduce the brittleness of absolute names. A relative package name is one that begins with one or more dots. A single dot means the current package, two dots mean the parent of the current package, and so on.

Table 2.2 presents a number of examples, assuming that the packages named foo, foo.bar, mypack, mypack.foo, mypack.foo.bar, mypack.foo.baz, mypack.bar, and mypack.bar.baz, have all been created.

Additional notes:

1. All packages in the hierarchy must exist.
2. Warning about nicknames: Unless you provide nicknames for your hierarchical packages (and we recommend against doing so because the number gets quite large), you can only use the names supplied. You cannot mix in nicknames or alternate names. cl-user is nickname of the common-lisp-user package. Consider the following:

      (defpackage :cl-user.foo)
   

   When the current package (the value of the variable *package*) is common-lisp-user, you might expect .foo to refer to cl-user.foo, but it does not. It actually refers to the non-existent package common-lisp-user.foo. Note that the purpose of nicknames is to provide shorter names in place of the longer names that are designed to be fully descriptive. The hope is that hierarchical packages makes longer names unnecessary and thus makes nicknames unnecessary.

3. Multiple dots can only appear at the beginning of a package name. For example, foo.bar..baz does not mean foo.baz – it is invalid. (Of course, it is perfectly legal to name a package foo.bar..baz, but cl:find-package will not process such a name to find foo.baz in the package hierarchy.)