Project author Jean-Philippe Paradis
Project type Library
Programming language Common Lisp
Status Ready-to-use
License Public Domain
Library type Data structure
Project complexity Simple
Latest release Version 1.0
Date 28 oct 2012
(Dec 2012 dist and later)
Status Available
Version Latest
Depends on Depended on by
Directly Nothing
Indirectly Nothing Nothing

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).

incognito-keywords » Some hypothetical examples

incognito keywords, or "ikeywords" for short, are useful targets for various kinds of dispatching.

(define (macro my-macro) ...)

;; 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 being a normal symbol
;; would very likely result in symbol conflicts.

(map 'alist ...)

(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!

incognito-keywords » API

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 and ensure and the macro defpackage. These symbols should be explicitly qualified. For example, ikeywords:defpackage instead of (:use #:ikeywords) or (:import-from #:ikeywords #:defpackage).

ikeywords live in the ikeyword package and are typically created implicitly with ikeywords:defpackage, but it's also possible to create some dynamically with ikeywords:ensure.

Macro 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 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 package => ikeyword-package

This convenience function simply returns the ikeyword package.

It's basically equivalent to (find-package '#:ikeyword).

incognito-keywords » 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 of this library could actually increase (definition) conflicts. So please carefully consider 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.