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in-package

in-package Macro

Syntax:

in-package name → package

Arguments and Values:

name—a string designator ; not evaluated.

package—the package named by name.

Description:

Causes the the package named by name to become the current package—that is, the value of *package*. If no such package already exists, an error of type package-error is signaled.

Everything in-package does is also performed at compile time if the call appears as a top level form.

Side Effects:

The variable *package* is assigned. If the in-package form is a top level form, this assignment also occurs at compile time.

Exceptional Situations:

An error of type package-error is signaled if the specified package does not exist.

See Also:

*package*

Expanded Reference: in-package​

Basic Usage: Switching the Current Package​

in-package sets *package* to the named package and returns it. The name is not evaluated.

(in-package "COMMON-LISP-USER")
==> #<PACKAGE "COMMON-LISP-USER">

*package*
==> #<PACKAGE "COMMON-LISP-USER">

Switching to a User-Defined Package​

The package must already exist before in-package is called.

(defpackage "MY-MODULE"
  (:use "COMMON-LISP"))

(in-package "MY-MODULE")
==> #<PACKAGE "MY-MODULE">

(package-name *package*)
;; => "MY-MODULE"

;; Switch back
(in-package "COMMON-LISP-USER")
==> #<PACKAGE "COMMON-LISP-USER">

Using a Symbol as the Name Argument​

Since the name is a string designator, a symbol may be used. Its symbol-name is taken.

(defpackage "DEMO-PKG" (:use "COMMON-LISP"))
(in-package demo-pkg)
==> #<PACKAGE "DEMO-PKG">

(in-package common-lisp-user)
==> #<PACKAGE "COMMON-LISP-USER">

Effect at Compile Time​

When in-package appears as a top-level form, it also takes effect at compile time. This is why source files typically begin with in-package after defpackage.

;; Typical file structure:
;; (defpackage "MY-SYSTEM" (:use "COMMON-LISP") (:export "RUN"))
;; (in-package "MY-SYSTEM")
;; (defun run () ...)

;; The in-package form ensures that all subsequent forms in the file
;; are read in the MY-SYSTEM package.