git clone 'https://github.com/avodonosov/local-package-aliases.git'

(ql:quickload :local-package-aliases)

Local Package Aliases

Allows to define inside of a package aliases to refer other packages. Provides a reader macro $ to use the aliases (active only in packages having alias mapping, and does not affect other code). Portable.

(ql:quickload :local-package-aliases)

(defpackage com.my-company.some-library
  (:use cl)
  (:export #:func))

(in-package #:com.my-company.some-library)

(defun func () "hello")

(defpackage some-application (:use cl))
(in-package #:some-application)
(local-package-aliases:set #:com.my-company.some-library #:lib
                           #:some.other.library #:olib)

(read-from-string "$lib:func")

;; => "hello"

;; The aliases are not global, they are scoped only to the package
;; where they are defined:

(in-package #:cl-user)
(read-from-string "$lib:func")
;; => ERROR There is no package named "$LIB" .

;; The $ reader macro is non-terminating,
;; therefore it is only activated when $
;; is on the beginning of a token.
;; $ in the middle of a token has no special
;; effect.
(in-package #:some-application)

(read-from-string "just-a-$-symbol")

;; The $ designates alias reference only if the
;; current package has alias mapping defined. If there
;; is no alias mapping in the current package, then
;; $ is interpreted as usually:

(local-package-aliases:set) ;; installs empty aliases mapping
(read-from-string "$-a-sybmol")
;; => $-A-SYMBOL

(in-package #:cl-user)
(read-from-string "$-a-sybmol")
;; => $-A-SYMBOL

;; Therefore it is safe to enable $ macro
;; globally, for example from Lisp init file,
;; without affecting the code using $ for other
;; purposes.

To enable the $ macro in your lisp session (may be put into the lisp initialization file): common-lisp (local-package-aliases:set-aliasing-reader *readtable*)

Another macro character than $ may be used. See the docstring for local-package-aliases:set-aliasing-reader for parameters description.

To return to the standard syntax: common-lisp (set-syntax-from-char #\$ #\$ *readtable* (copy-readtable nil))

To make the $ macro enabled when your ASDF system is compiled by other people, use the :acound-compile argument:

(asdf:defsystem #:some-application
  :depends-on (#:local-package-aliases
  :around-compile "local-package-aliases:call-with-aliasing-readtable"
  :components ((:file "some-application")))

SLIME support

SLIME assumes standard readtable when meets tokens like pkg:symb and doesn't undersdand our aliases.

In result SLIME symbol completion, slime-edit-definition, function arguments hints do not work out of box for aliased tokens like $lib:func.

The solution we found is to hook into swank, and wrap evaluation of every SLIME request with temporary adding the aliases defined in the current package as nicknames for their corresponding packages. So, during dynamic extent of every slime request, the aliases become real package nicknames and SLIME can handle them as usually.

It must be noted that this solution is not entierly transarent: when working from SLIME not only reader understands the aliases, but also (find-package :$lib) will find the package. But of course during normal run-time only reader knows about the aliases.

Functions hook-into-swank and unhook-from-swank enable/disable this SLIME support.

To have the SIME support enabled automatically add the following to your ~/.swank.lisp: common-lisp (when (find-package :local-package-aliases) (funcall (read-from-string "local-package-aliases:hook-into-swank"))) Or this in ~/.emacs: common-lisp (add-hook 'slime-connected-hook (lambda () (slime-eval '(cl:when (cl:find-package :local-package-aliases) (cl:funcall (cl:read-from-string "local-package-aliases:hook-into-swank"))))))

Other Package Aliasing Approaches

Here is some information, solutions and ideas I encountered recently related to package aliases.

The solutions vary in: - whether the aliases only honored by reader, or they also affect functions like cl:find-package, cl:find-symbol - is the solution a portable Common Lisp or it relies on patches or language extensions - whether the aliases are scoped to a package, or somehow else - whether the solution is specific about aliasing scheme, or it's a lower-level tool allowing to build various aliasing approaches.

cl-package-aliases - http://www.cliki.net/cl-package-aliases

Provides patches for 5 lisp implementations to introduce aliases. Aliases are scoped to package and visible both for reader and for standard functions like cl:find-symbol.

package-renaming - http://common-lisp.net/gitweb?p=users/frideau/package-renaming.git;a=tree

Tools based on cl:rename-package to temporary give packages desired short names/nicknames. Portable. To make the renaming local it is expected to be used with the ASDF's :acound-compile argument.

CL language extensions

There were discussions to develop a CL language extension and propose it to CL vendors. The extension might be a hook called by CL to resolve package prefix. I.e. when CL encounteres a token like pkg:symbol it calls the hook with “pkg” string and the hook should return a package object or maybe just a string designating real package name. Such hook may be called *package-prefix-resolver*.

Alternatively the hook may be passed the full token “pkg:symbol” and be responsible to resolve both package name and symbol. Such hook may be named *parse-token-hook*.

There were considerations whether these hooks should be called only form reader or by cl:find-sybmol and other functions. Sketch for a CDR: http://paste.lisp.org/display/133561 Discussions on the #lisp irc channel: http://ccl.clozure.com/irc-logs/lisp/2012-11/lisp-2012.11.05.txt http://ccl.clozure.com/irc-logs/lisp/2013-01/lisp-2013.01.06.txt

One more possible language extension would be to allow to fully substitute the lisp reader. In this case there might be are public library implementing fully compliant CL reader. Lisp implementation will delegate functions like cl:read, cl:read-delimeted-list, cl:set-syntax-from-char and others to the pluggable reader. The reader by default honors cl:*readtable*, cl:*package* and other variables, but also allows any custom hooks we need, such as described above parse-token-hook and/or package-prefix-resolver. It must be noted that interface between CL and such a pluggable reader will consist of many functions. Also, the reader should come with it's own implementations for all the reader macros, because standard reader macros are not implemented in terms of public cl:* functions, but use private, not-exported functions of the CL reader, such as reat-token.

If speak about pluggable reader, it's necessary to mention the reader-interception project: http://common-lisp.net/cgi-bin/gitweb.cgi?p=users/frideau/reader-interception.git;a=tree;js=1

It's a portable solution allowing to plug-in your own reader. It relies on the trick to look at the first character of input, configure this character temporary as a reader macro, and then this reader macro may read the full input stream according to any rules.


The local-package-aliases approach with reader macro seems to be a decent approach, especially as the syntax change only affects packages with explicitly configured aliasing maps.

It is comparable by convenience with package-renaming.

Advantage of local-package-aliases is that it may be enabled once and forewer in the Lisp initialization file, while packag-renaming will require you to manually rename packages every time you switch projects or subsystems during or at the beginning of Lisp session.

In my opinion a form of package aliasing deserves to be introduced as a CL extension into all implementations.

The language extension may be specific, targeting only package aliases (like cl-package-aliases project proposes). It will encourage consistent coding practice accross all the CL programs.

To simplify adoption of the extension by the CL implementations, I believe it would be enought to have aliasing only in reader. Calls to cl:find-package are rare, we can pass full package names to it. On the other hand, if cl:find-package is unaware of aliases, it may complicate support by SLIME.

As for more low-level language extenstions, like pluggable reader or various hooks, I would welcome them too, just to make Lisp more programmable and allow programmers to solve their needs simpler.


Anton Vodonosov, avodonosov@yandex.ru