CLHS: Function SHADOW

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Function SHADOW

Syntax:

shadow symbol-names `&optional` package => t

Arguments and Values:

symbol-names---a designator for a list of string designators.

package---a package designator. The default is the current package.

Description:

shadow assures that symbols with names given by symbol-names are present in the package.

Specifically, package is searched for symbols with the names supplied by symbol-names. For each such name, if a corresponding symbol is not present in package (directly, not by inheritance), then a corresponding symbol is created with that name, and inserted into package as an internal symbol. The corresponding symbol, whether pre-existing or newly created, is then added, if not already present, to the shadowing symbols list of package.

Examples:

     (package-shadowing-symbols (make-package 'temp)) =>  NIL
     (find-symbol 'car 'temp) =>  CAR, :INHERITED
     (shadow 'car 'temp) =>  T
     (find-symbol 'car 'temp) =>  TEMP::CAR, :INTERNAL
     (package-shadowing-symbols 'temp) =>  (TEMP::CAR)

     (make-package 'test-1) =>  #<PACKAGE "TEST-1">
     (intern "TEST" (find-package 'test-1)) =>  TEST-1::TEST, NIL
     (shadow 'test-1::test (find-package 'test-1)) =>  T
     (shadow 'TEST (find-package 'test-1)) =>  T
     (assert (not (null (member 'test-1::test (package-shadowing-symbols
                                                (find-package 'test-1))))))

     (make-package 'test-2) =>  #<PACKAGE "TEST-2">
     (intern "TEST" (find-package 'test-2)) =>  TEST-2::TEST, NIL
     (export 'test-2::test (find-package 'test-2)) =>  T
     (use-package 'test-2 (find-package 'test-1))    ;should not error

Side Effects:

shadow changes the state of the package system in such a way that the package consistency rules do not hold across the change.

Affected By:

Current state of the package system.

Exceptional Situations: None.

See Also:

package-shadowing-symbols, Section 11.1 (Package Concepts)

Notes:

If a symbol with a name in symbol-names already exists in package, but by inheritance, the inherited symbol becomes shadowed[3] by a newly created internal symbol.

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

- SHADOW-ALREADY-PRESENT
- PACKAGE-FUNCTION-CONSISTENCY:MORE-PERMISSIVE
- SHADOW-ALREADY-PRESENT:WORKS

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