provide module-name => implementation-dependent
require module-name &optional pathname-list => implementation-dependent
Arguments and Values:
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*)
provide modifies *modules*.
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.
*modules*, Section 19.1.2 (Pathnames as Filenames)
The functions provide and require are deprecated.
If a module consists of a single package, it is customary for the package and module names to be the same.