#### 24.2.11 provide, require [Function]

`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.

#### Description::

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.

#### Examples::

    ;;; 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*)

#### Side Effects::

provide modifies *modules*.

#### Affected By::

The specific action taken by require is affected by calls to provide (or, in general, any changes to the value of *modules*).

#### Exceptional Situations::

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.

#### See Also::

*modules*,

Pathnames as Filenames

#### Notes::

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.