CLHS: Function PROVIDE, REQUIRE

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Function PROVIDE, REQUIRE

Syntax:

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*, Section 19.1.2 (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.

The following X3J13 cleanup issues, not part of the specification, apply to this section:

- FILE-OPEN-ERROR:SIGNAL-FILE-ERROR
- REQUIRE-PATHNAME-DEFAULTS-YET-AGAIN:RESTORE-ARGUMENT
- REQUIRE-PATHNAME-DEFAULTS-AGAIN:X3J13-DEC-91

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