symbol-names—a designator for a list of string designators.
package—a package designator. The default is the current package.
shadow assures that symbols with names given
by symbol-names are present
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.
(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
shadow changes the state of the package system in such a
way that the package consistency rules do not hold across the change.
Current state of the package system.
package-shadowing-symbols, Section 11.1 (Package Concepts)
If a symbol with a name in symbol-names already exists in package, but by inheritance, the inherited symbol becomes shadowed3 by a newly created internal symbol.