đź“ťCommon Lisp: packages and symbols
symbols
symbol without a colon is an unqualified name
symbol with one colon can only refer to exported (public) symbols
symbol with double-colon can refer to unexported symbols
keyword symbols start with colon and are interned in
KEYWORDpackage and automatically exporteduninterned symbols are written with a leading
#:. Every time the reader reads a name starting with#:, it creates a new symbol
accessible: all the symbols that can be found in a given package with
find-symbol(= symbols that can be referred to with unqualified names when the package is current)present: symbol is contained in package’s name-to-symbol table
The package in which a symbol is first interned (by the reader) is home package
A package inherits symbols from other packages by using the other packages. Only external symbols are inherited. A symbol is made external by exporting (also makes it accessible via single-colon name).
For each name, there can only be one symbol max. A symbol can be made shadowing which makes it shadow other symbols with the same name. Each package maintains a list of shadowing symbols.
A symbol can be imported by adding it to the name-to-symbol table
A symbol can be uninterned from a package—removed from its name-to-symbol and shadowing tables
a symbol that is not present in any package is called an uninterned symbol, and can no longer be read by the reader
Package system in common lisp is only exporting symbols, not functions or variables.
;; define package
(defpackage :package.name
(:use :common-lisp :package2)
;; export symbols
(:export
:symbol1
:symbol2)
;; import symbols
(:import-from :other.package.name :symbol3 :symbol4)
;; shadow a symbol (e.g., from :use above)
;;
;; This creates a new 'symbol5 and adds it to package-to-name table
;; of package.name and to shadowing list
(:shadow :symbol5)
;; Shadowing import (makes symbol-name from other packages
;; inaccessible)
(:shadowing-import-from :package-name :symbol-name))