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incognito-keywords introduces a new kind of keyword that looks just
like any non-keyword symbol and allows safe usage of convenient but
clashy symbol names by multiple libraries without conflicts through
sharing. Some names that might benefit are (alist blist plist macro
operator index &doc &decl &rest+ &destructure &ignored &ignorable).
Some hypothetical examples
incognito keywords, or "ikeywords" for short, are useful targets for
various kinds of dispatching.
(define (macro my-macro) ...) ; MACRO being an ikeyword
;; blends much better with:
(define (variable my-variable) ...) ; VARIABLE is exported from CL.
;; than would:
(define (:macro my-macro))
;; And the following:
(define (macro my-macro) ...) ; MACRO a normal symbol
;; would very likely result in symbol conflicts.
(map 'alist ...) ; ALIST being an ikeyword
;; INDEX, &IGNORED and PLIST being ikeywords
(do-for ((i (index :from 1))
(((&ignored key) value) (plist my-plist)))
(ikeywords:defpackage #:do-for.ikeywords
(:export #:index
(defpackage #:do-for-user-package
(:use #:cl #:do-for-ikeywords)
(:import-from #:do-for #:do-for))
(locate 'macro "my-macro")
In the examples above, DEFINE, MAP, DO-FOR and LOCATE could come from
different libraries by different authors. If they all use ikeywords as
appropriate, then their users can use all these libraries from one
package without symbol conflicts!
Usage of incognito-keywords is very easy!
First of all, in the way of packages there's the INCOGNITO-KEYWORDS
package, which is also nicknamed IKEYWORDS. It exports the functions
(PACKAGE ENSURE IKEYWORDP) and the macro DEFPACKAGE. These symbols
should be explicitly qualified. For example, ikeywords:defpackage
instead of (:use #:ikeywords) or (:import-from #:ikeywords
ikeywords live in the IKEYWORD package (also nicknamed "I") and are
typically created implicitly with ikeywords:defpackage, but it's also
possible to create some dynamically with ikeywords:ensure.
macro ikeywords:DEFPACKAGE name &rest options => new-or-redefined-package
A very simplified version of cl:defpackage dedicated to creation of
"ikeyword packages". The syntax is just like cl:defpackage, except
that only the :export, :nicknames, :documentation and :size options
are supported. The package will implicitly use the IKEYWORD package.
All the symbol names in :export clauses will be passed to ENSURE.
The :nicknames, :documentation and :size options are passed straight
through to cl:defpackage.
It's possible to obtain a list of all ikeyword packages with:
(package-used-by-list (ikeywords:package))
function ikeywords:ENSURE name => new-or-existing-ikeyword
If NAME already names an ikeyword (a symbol in the IKEYWORD
package), then return that ikeyword.
Else, create the ikeyword (interning a symbol with that name in the
IKEYWORD package), immediately export it (from the IKEYWORD
package), then return the new ikeyword.
Attempting to create an ikeyword with the name of one of the 978
symbols in the COMMON-LISP package is an error, as this would almost
inevitably result in symbol conflicts, which would defeat the whole
point of ikeywords!
function ikeywords:PACKAGE => ikeyword-package
This convenience function simply returns the IKEYWORD package.
Basically equivalent to (find-package '#:ikeyword).
function ikeywords:IKEYWORDP object => generalized-boolean
This convenience function simply returns true if the OBJECT is a
symbol and its home package (as returned by SYMBOL-PACKAGE) is the
IKEYWORD package, else it returns false.
Restrictions to avoid definition conflicts
incognito-keywords' reason to exist is to allow libraries to make use
of some very desirable symbol names, while avoiding the excessive
symbol conflicts this would normally incur. HOWEVER, INCORRECT USAGE
please carefully read and understand the following:
Libraries should not create global definitions for Common Lisp
functions, macros, SETF expanders, etc. on ikeywords, as any two
libraries that do this can't be safely loaded in the same image.
However, if a library creates a new kind of definition in another
"namespace", then this library can safely create such definitions on
these symbols. However, if that library exports a way to create such
definitions, then users of that library can't safely create such
definitions on ikeywords.
For this reason, libraries in this situation should provide any
appropriate definitions on ikeywords using their new exported
definition mechanisms, and prohibit their users, through mechanism
and/or policy, from providing any new definitions on those ikeywords.
This library is in the Public Domain.
See the UNLICENSE file for details.