provide module-name ⇒ implementation-dependent
require module-name &optional pathname-list ⇒ implementation-dependent
| module-name | a string designator. |
| pathname-list | nil, or a designator for a non-empty list of pathname designators. The default is nil. |
provide adds the module-name to the list held by *modules*, if such a name is not already present.
require tests for the presence of the module-name in the list held by *modules*. If it is present, require immediately returns.
Otherwise, an attempt is made to load an appropriate set of files as follows: The pathname-list argument, if non-nil, specifies a list of pathnames to be loaded in order, from left to right. If the pathname-list is nil, an implementation-dependent mechanism will be invoked in an attempt to load the module named module-name; if no such module can be loaded, an error of type error is signaled.
Both functions use string= to test for the presence of a module-name.
;;; This illustrates a nonportable use of REQUIRE, because it
;;; depends on the implementation-dependent file-loading mechanism.
(require "CALCULUS")
;;; This use of REQUIRE is nonportable because of the literal
;;; physical pathname.
(require "CALCULUS" "/usr/lib/lisp/calculus")
;;; One form of portable usage involves supplying a logical pathname,
;;; with appropriate translations defined elsewhere.
(require "CALCULUS" "lib:calculus")
;;; Another form of portable usage involves using a variable or
;;; table lookup function to determine the pathname, which again
;;; must be initialized elsewhere.
(require "CALCULUS" *calculus-module-pathname*)
The specific action taken by require is affected by calls to provide (or, in general, any changes to the value of *modules*).
Should signal an error of type type-error if module-name is not a string designator.
If require fails to perform the requested operation due to a problem while interacting with the file system, an error of type file-error is signaled.
An error of type file-error might be signaled if any pathname in pathname-list is a designator for a wild pathname.