Change install- and uninstall- to -install and -uninstall.

[bpt/emacs.git] / lisp / emacs-lisp / advice.el

;;; advice.el --- an overloading mechanism for Emacs Lisp functions

;; Copyright (C) 1993, 1994 Free Software Foundation, Inc.

;; Author: Hans Chalupsky <hans@cs.buffalo.edu>
;; Created: 12 Dec 1992
;; Version: advice.el,v 2.11 1994/02/24 22:51:43 hans Exp
;; Keywords: extensions, lisp, tools

;; This file is part of GNU Emacs.

;; GNU Emacs is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation; either version 2, or (at your option)
;; any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs; see the file COPYING.  If not, write to
;; the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.

;; LCD Archive Entry:
;; advice|Hans Chalupsky|hans@cs.buffalo.edu|
;; Overloading mechanism for Emacs Lisp functions|
;; 1994/02/24 22:51:43|2.11|~/packages/advice.el.Z|


;;; Commentary:

;; NOTE: This documentation is slightly out of date. In particular, all the
;; references to Emacs-18 are obsolete now, because it is not any longer
;; supported by this version of Advice. An up-to-date version will soon be
;; available as an info file (thanks to the kind help of Jack Vinson and
;; David M. Smith).

;; @ Introduction:
;; ===============
;; This package implements a full-fledged Lisp-style advice mechanism
;; for Emacs Lisp. Advice is a clean and efficient way to modify the 
;; behavior of Emacs Lisp functions without having to keep  personal
;; modified copies of such functions around. A great number of such 
;; modifications can be achieved by treating the original function as a 
;; black box and specifying a different execution environment for it 
;; with a piece of advice. Think of a piece of advice as a kind of fancy
;; hook that you can attach to any function/macro/subr.

;; @ Highlights:
;; =============
;; - Clean definition of multiple, named before/around/after advices
;;   for functions, macros, subrs and special forms
;; - Full control over the arguments an advised function will receive,
;;   the binding environment in which it will be executed, as well as the
;;   value it will return.
;; - Allows re/definition of interactive behavior for functions and subrs
;; - Every piece of advice can have its documentation string which will be 
;;   combined with the original documentation of the advised function at
;;   call-time of `documentation' for proper command-key substitution.
;; - The execution of every piece of advice can be protected against error
;;   and non-local exits in preceding code or advices.
;; - Simple argument access either by name, or, more portable but as
;;   efficient, via access macros
;; - Allows the specification of a different argument list for the advised
;;   version of a function.
;; - Advised functions can be byte-compiled either at file-compile time
;;   (see preactivation) or activation time.
;; - Separation of advice definition and activation
;; - Provides generally accessible function definition (after) hooks
;; - Forward advice is possible (an application of definition hooks), that is
;;   as yet undefined or autoload functions can be advised without having to
;;   preload the file in which they are defined. 
;; - Forward redefinition is possible because around advice can be used to
;;   completely redefine a function.
;; - A caching mechanism for advised definition provides for cheap deactivation
;;   and reactivation of advised functions.
;; - Preactivation allows efficient construction and compilation of advised
;;   definitions at file compile time without giving up the flexibility of
;;   the advice mechanism.
;; - En/disablement mechanism allows the use of  different "views" of advised
;;   functions depending on what pieces of advice are currently en/disabled
;; - Provides manipulation mechanisms for sets of advised functions via 
;;   regular expressions that match advice names
;; - Allows definition of load-hooks for arbitrary Emacs Lisp files without
;;   modification of these files

;; @ How to get Advice for Emacs-18:
;; =================================
;; `advice18.el', a version of Advice that also works in Emacs-18 is available
;; either via anonymous ftp from `ftp.cs.buffalo.edu (128.205.32.9)' with 
;; pathname `/pub/Emacs/advice18.el', or from one of the Emacs Lisp archive
;; sites, or send email to <hans@cs.buffalo.edu> and I'll mail it to you.

;; @ Overview, or how to read this file:
;; =====================================
;; NOTE: This documentation is slightly out of date. In particular, all the
;; references to Emacs-18 are obsolete now, because it is not any longer
;; supported by this version of Advice. An up-to-date version will soon be
;; available as an info file (thanks to the kind help of Jack Vinson and
;; David M. Smith). Until then you can use `outline-mode' to help you read
;; this documentation (set `outline-regexp' to `";; @+"').
;;
;; The four major sections of this file are:
;;
;;   @ This initial information       ...installation, customization etc.
;;   @ Advice documentation:          ...general documentation
;;   @ Foo games: An advice tutorial  ...teaches about Advice by example
;;   @ Advice implementation:         ...actual code, yeah!!
;;
;; The latter three are actual headings which you can search for
;; directly in case `outline-mode' doesn't work for you.

;; @ Restrictions:
;; ===============
;; - This version of Advice only works for Emacs-19 or Lucid Emacs.
;; - Advised functions/macros/subrs will only exhibit their advised behavior
;;   when they are invoked via their function cell. This means that advice will
;;   not work for the following:
;;   + advised subrs that are called directly from other subrs or C-code 
;;   + advised subrs that got replaced with their byte-code during 
;;     byte-compilation (e.g., car)
;;   + advised macros which were expanded during byte-compilation before
;;     their advice was activated.

;; @ Known bug:
;; ============
;; - Using automatic activation of (forward) advice will break the
;;   function `interactive-p' when it is used in the body of a `catch'
;;   (this problem will go away once automatic advice activation gets
;;   supported by built-in functions).

;; @ Credits:
;; ==========
;; This package is an extension and generalization of packages such as
;; insert-hooks.el written by Noah S. Friedman, and advise.el written by
;; Raul J. Acevedo. Some ideas used in here come from these packages,
;; others come from the various Lisp advice mechanisms I've come across
;; so far, and a few are simply mine.

;; @ Comments, suggestions, bug reports:
;; =====================================
;; If you find any bugs, have suggestions for new advice features, find the
;; documentation wrong, confusing, incomplete, or otherwise unsatisfactory,
;; have any questions about Advice, or have otherwise enlightening
;; comments feel free to send me email at <hans@cs.buffalo.edu>.

;; @ Safety Rules and Emergency Exits:
;; ===================================
;; Before we begin: CAUTION!!
;; Advice provides you with a lot of rope to hang yourself on very
;; easily accessible trees, so, here are a few important things you
;; should know: Once Advice has been started with `ad-start-advice' it
;; generates advised definitions of the `documentation' function, and,
;; if definition hooks are enabled (e.g., for forward advice), also of
;; `defun', `defmacro' and `fset' (if you use Jamie Zawinski's (jwz)
;; optimizing byte-compiler as standardly used in Emacs-19 and
;; Lucid Emacs-19 (Lemacs), then enabling definition hooks will also
;; redefine the `byte-code' subr). All these changes can be undone at
;; any time with `M-x ad-stop-advice'.
;; 
;; If you experience any strange behavior/errors etc. that you attribute to
;; Advice or to some ill-advised function do one of the following:

;; - M-x ad-deactivate FUNCTION (if you have a definite suspicion what
;;                               function gives you problems)
;; - M-x ad-deactivate-all      (if you don't have a clue what's going wrong)
;; - M-x ad-stop-advice         (if you think the problem is related to the
;;                               advised functions used by Advice itself)
;; - M-x ad-recover-normality   (for real emergencies)
;; - If none of the above solves your Advice-related problem go to another
;;   terminal, kill your Emacs process and send me some hate mail.

;; The first three measures have restarts, i.e., once you've figured out
;; the problem you can reactivate advised functions with either `ad-activate',
;; `ad-activate-all', or `ad-start-advice'. `ad-recover-normality' unadvises
;; everything so you won't be able to reactivate any advised functions, you'll
;; have to stick with their standard incarnations for the rest of the session.

;; IMPORTANT: With Advice loaded always do `M-x ad-deactivate-all' before
;; you byte-compile a file, because advised special forms and macros can lead
;; to unwanted compilation results. When you are done compiling use
;; `M-x ad-activate-all' to go back to the advised state of all your 
;; advised functions.

;; RELAX: Advice is pretty safe even if you are oblivious to the above.
;; I use it extensively and haven't run into any serious trouble in a long
;; time. Just wanted you to be warned.

;; @ Customization:
;; ================
;; Part of the advice magic does not start until you call `ad-start-advice'
;; which you can either do interactively, explicitly in your .emacs, or by
;; putting
;;
;;    (setq ad-start-advice-on-load t)
;;
;; into your .emacs which will automatically start advice when the file gets
;; loaded.

;; If you want to be able to forward advise functions, that is to advise them
;; when they are not yet defined or defined as autoloads, then you should put 
;; the following into your .emacs
;;
;;    (setq ad-activate-on-definition t)
;;
;; which will activate all advice at the time the function gets actually 
;; defined/loaded. The value of this variable will not have any effect until
;; `ad-start-advice' gets executed.

;; Look at the documentation of `ad-redefinition-action' for possible values
;; of this variable. Its default value is `warn' which will print a warning
;; message when an already defined advised function gets redefined with a
;; new original definition and de/activated.

;; @ Motivation:
;; =============
;; Before I go on explaining how advice works, here are four simple examples
;; how this package can be used. The first three are very useful, the last one
;; is just a joke:

;;(defadvice switch-to-buffer (before existing-buffers-only activate)
;;  "When called interactively switch to existing buffers only, unless 
;;when called with a prefix argument."
;;  (interactive 
;;   (list (read-buffer "Switch to buffer: " (other-buffer) 
;;                      (null current-prefix-arg)))))
;;
;;(defadvice switch-to-buffer (around confirm-non-existing-buffers activate)
;;  "Switch to non-existing buffers only upon confirmation."
;;  (interactive "BSwitch to buffer: ")
;;  (if (or (get-buffer (ad-get-arg 0))
;;          (y-or-n-p (format "`%s' does not exist, create? " (ad-get-arg 0))))
;;      ad-do-it))
;;
;;(defadvice find-file (before existing-files-only activate)
;;  "Find existing files only"
;;  (interactive "fFind file: "))
;;
;;(defadvice car (around interactive activate)
;;  "Make `car' an interactive function."
;;   (interactive "xCar of list: ")
;;   ad-do-it
;;   (if (interactive-p)
;;       (message "%s" ad-return-value)))


;; @ Advice documentation:
;; =======================
;; Below is general documentation of the various features of advice. For more
;; concrete examples check the corresponding sections in the tutorial part.

;; @@ Terminology:
;; ===============
;; - Emacs, Emacs-19: FSF's version of Emacs with major version 19
;; - Lemacs: Lucid's version of Emacs with major version 19
;; - v18: Any Emacs with major version 18 or built as an extension to that
;;        (such as Epoch)
;; - v19: Any Emacs with major version 19
;; - jwz: Jamie Zawinski - keeper of Lemacs and creator of the optimizing
;;        byte-compiler used in v19s.
;; - Advice: The name of this package.
;; - advices: Short for "pieces of advice".

;; @@ Defining a piece of advice with `defadvice':
;; ===============================================
;; The main means of defining a piece of advice is the macro `defadvice',
;; there is no interactive way of specifying a piece of advice.  A call to
;; `defadvice' has the following syntax which is similar to the syntax of
;; `defun/defmacro':
;;
;; (defadvice <function> (<class> <name> [<position>] [<arglist>] {<flags>}*)
;;   [ [<documentation-string>] [<interactive-form>] ]
;;   {<body-form>}* )

;; <function> is the name of the function/macro/subr to be advised.

;; <class> is the class of the advice which has to be one of `before',
;; `around', `after', `activation' or `deactivation' (the last two allow
;; definition of special act/deactivation hooks).

;; <name> is the name of the advice which has to be a non-nil symbol.
;; Names uniquely identify a piece of advice in a certain advice class,
;; hence, advices can be redefined by defining an advice with the same class
;; and name. Advice names are global symbols, hence, the same name space
;; conventions used for function names should be applied.

;; An optional <position> specifies where in the current list of advices of
;; the specified <class> this new advice will be placed. <position> has to
;; be either `first', `last' or a number that specifies a zero-based
;; position (`first' is equivalent to 0). If no position is specified
;; `first' will be used as a default. If this call to `defadvice' redefines
;; an already existing advice (see above) then the position argument will
;; be ignored and the position of the already existing advice will be used.

;; An optional <arglist> which has to be a list can be used to define the
;; argument list of the advised function. This argument list should of
;; course be compatible with the argument list of the original function,
;; otherwise functions that call the advised function with the original
;; argument list in mind will break. If more than one advice specify an
;; argument list then the first one (the one with the smallest position)
;; found in the list of before/around/after advices will be used.

;; <flags> is a list of symbols that specify further information about the
;; advice. All flags can be specified with unambiguous initial substrings.
;;   `activate': Specifies that the advice information of the advised
;;              function should be activated right after this advice has been
;;              defined. In forward advices `activate' will be ignored. 
;;   `protect': Specifies that this advice should be protected against
;;              non-local exits and errors in preceding code/advices.
;;   `compile': Specifies that the advised function should be byte-compiled.
;;              This flag will be ignored unless `activate' is also specified.
;;   `disable': Specifies that the defined advice should be disabled, hence,
;;              it will not be used in an activation until somebody enables it.
;;   `preactivate': Specifies that the advised function should get preactivated
;;              at macro-expansion/compile time of this `defadvice'. This
;;              generates a compiled advised definition according to the
;;              current advice state which will be used during activation
;;              if appropriate. Only use this if the `defadvice' gets
;;              actually compiled (with a v18 byte-compiler put the `defadvice'
;;              into the body of a `defun' to accomplish proper compilation).

;; An optional <documentation-string> can be supplied to document the advice.
;; On call of the `documentation' function it will be combined with the
;; documentation strings of the original function and other advices.

;; An optional <interactive-form> form can be supplied to change/add
;; interactive behavior of the original function. If more than one advice
;; has an `(interactive ...)' specification then the first one (the one
;; with the smallest position) found in the list of before/around/after
;; advices will be used.

;; A possibly empty list of <body-forms> specifies the body of the advice in
;; an implicit progn. The body of an advice can access/change arguments,
;; the return value, the binding environment, and can have all sorts of 
;; other side effects.

;; @@ Assembling advised definitions:
;; ==================================
;; Suppose a function/macro/subr/special-form has N pieces of before advice,
;; M pieces of around advice and K pieces of after advice. Assuming none of
;; the advices is protected, its advised definition will look like this
;; (body-form indices correspond to the position of the respective advice in
;; that advice class):

;;    ([macro] lambda <arglist>
;;       [ [<advised-docstring>] [(interactive ...)] ]
;;       (let (ad-return-value)
;;         {<before-0-body-form>}*
;;               ....
;;         {<before-N-1-body-form>}*
;;         {<around-0-body-form>}*
;;            {<around-1-body-form>}*
;;                  ....
;;               {<around-M-1-body-form>}*
;;                  (setq ad-return-value
;;                        <apply original definition to <arglist>>)
;;               {<other-around-M-1-body-form>}*
;;                  ....
;;            {<other-around-1-body-form>}*
;;         {<other-around-0-body-form>}*
;;         {<after-0-body-form>}*
;;               ....
;;         {<after-K-1-body-form>}*
;;         ad-return-value))

;; Macros and special forms will be redefined as macros, hence the optional
;; [macro] in the beginning of the definition.

;; <arglist> is either the argument list of the original function or the
;; first argument list defined in the list of before/around/after advices.
;; The values of <arglist> variables can be accessed/changed in the body of
;; an advice by simply referring to them by their original name, however,
;; more portable argument access macros are also provided (see below).  For
;; subrs/special-forms for which neither explicit argument list definitions
;; are available, nor their documentation strings contain such definitions
;; (as they do v19s), `(&rest ad-subr-args)' will be used.

;; <advised-docstring> is an optional, special documentation string which will
;; be expanded into a proper documentation string upon call of `documentation'.

;; (interactive ...) is an optional interactive form either taken from the
;; original function or from a before/around/after advice. For advised
;; interactive subrs that do not have an interactive form specified in any
;; advice we have to use (interactive) and then call the subr interactively
;; if the advised function was called interactively, because the
;; interactive specification of subrs is not accessible. This is the only
;; case where changing the values of arguments will not have an affect
;; because they will be reset by the interactive specification of the subr.
;; If this is a problem one can always specify an interactive form in a
;; before/around/after advice to gain control over argument values that
;; were supplied interactively.
;; 
;; Then the body forms of the various advices in the various classes of advice
;; are assembled in order.  The forms of around advice L are normally part of
;; one of the forms of around advice L-1. An around advice can specify where
;; the forms of the wrapped or surrounded forms should go with the special
;; keyword `ad-do-it', which will be substituted with a `progn' containing the
;; forms of the surrounded code.

;; The innermost part of the around advice onion is 
;;      <apply original definition to <arglist>>
;; whose form depends on the type of the original function. The variable
;; `ad-return-value' will be set to its result. This variable is visible to
;; all pieces of advice which can access and modify it before it gets returned.
;; 
;; The semantic structure of advised functions that contain protected pieces
;; of advice is the same. The only difference is that `unwind-protect' forms
;; make sure that the protected advice gets executed even if some previous
;; piece of advice had an error or a non-local exit. If any around advice is
;; protected then the whole around advice onion will be protected.

;; @@ Argument access in advised functions:
;; ========================================
;; As already mentioned, the simplest way to access the arguments of an
;; advised function in the body of an advice is to refer to them by name. To
;; do that, the advice programmer needs to know either the names of the
;; argument variables of the original function, or the names used in the
;; argument list redefinition given in a piece of advice. While this simple
;; method might be sufficient in many cases, it has the disadvantage that it
;; is not very portable because it hardcodes the argument names into the
;; advice. If the definition of the original function changes the advice
;; might break even though the code might still be correct. Situations like
;; that arise, for example, if one advises a subr like `eval-region' which
;; gets redefined in a non-advice style into a function by the edebug
;; package. If the advice assumes `eval-region' to be a subr it might break
;; once edebug is loaded. Similar situations arise when one wants to use the
;; same piece of advice across different versions of Emacs. Some subrs in a
;; v18 Emacs are functions in v19 and vice versa, but for the most part the
;; semantics remain the same, hence, the same piece of advice might be usable
;; in both Emacs versions.

;; As a solution to that advice provides argument list access macros that get
;; translated into the proper access forms at activation time, i.e., when the
;; advised definition gets constructed. Access macros access actual arguments
;; by position regardless of how these actual argument get distributed onto
;; the argument variables of a function. The rational behind this is that in
;; Emacs Lisp the semantics of an argument is strictly determined by its
;; position (there are no keyword arguments).

;; Suppose the function `foo' is defined as
;;
;;    (defun foo (x y &optional z &rest r) ....)
;;
;; and is then called with
;;
;;    (foo 0 1 2 3 4 5 6)

;; which means that X=0, Y=1, Z=2 and R=(3 4 5 6). The assumption is that
;; the semantics of an actual argument is determined by its position. It is
;; this semantics that has to be known by the advice programmer. Then s/he
;; can access these arguments in a piece of advice with some of the
;; following macros (the arrows indicate what value they will return):

;;    (ad-get-arg 0) -> 0
;;    (ad-get-arg 1) -> 1
;;    (ad-get-arg 2) -> 2
;;    (ad-get-arg 3) -> 3
;;    (ad-get-args 2) -> (2 3 4 5 6)
;;    (ad-get-args 4) -> (4 5 6)

;; `(ad-get-arg <position>)' will return the actual argument that was supplied
;; at <position>, `(ad-get-args <position>)' will return the list of actual
;; arguments supplied starting at <position>. Note that these macros can be
;; used without any knowledge about the form of the actual argument list of
;; the original function.

;; Similarly, `(ad-set-arg <position> <value-form>)' can be used to set the
;; value of the actual argument at <position> to <value-form>. For example,
;;
;;   (ad-set-arg 5 "five")
;;
;; will have the effect that R=(3 4 "five" 6) once the original function is
;; called. `(ad-set-args <position> <value-list-form>)' can be used to set
;; the list of actual arguments starting at <position> to <value-list-form>.
;; For example,
;;
;;   (ad-set-args 0 '(5 4 3 2 1 0))
;;
;; will have the effect that X=5, Y=4, Z=3 and R=(2 1 0) once the original
;; function is called.

;; All these access macros are text macros rather than real Lisp macros. When
;; the advised definition gets constructed they get replaced with actual access
;; forms depending on the argument list of the advised function, i.e., after
;; that argument access is in most cases as efficient as using the argument
;; variable names directly.

;; @@@ Accessing argument bindings of arbitrary functions:
;; =======================================================
;; Some functions (such as `trace-function' defined in trace.el) need a
;; method of accessing the names and bindings of the arguments of an
;; arbitrary advised function. To do that within an advice one can use the
;; special keyword `ad-arg-bindings' which is a text macro that will be
;; substituted with a form that will evaluate to a list of binding
;; specifications, one for every argument variable.  These binding
;; specifications can then be examined in the body of the advice.  For
;; example, somewhere in an advice we could do this:
;;
;;   (let* ((bindings ad-arg-bindings)
;;          (firstarg (car bindings))
;;          (secondarg (car (cdr bindings))))
;;     ;; Print info about first argument
;;     (print (format "%s=%s (%s)"
;;                    (ad-arg-binding-field firstarg 'name)
;;                    (ad-arg-binding-field firstarg 'value)
;;                    (ad-arg-binding-field firstarg 'type)))
;;     ....)
;;
;; The `type' of an argument is either `required', `optional' or `rest'.
;; Wherever `ad-arg-bindings' appears a form will be inserted that evaluates
;; to the list of bindings, hence, in order to avoid multiple unnecessary
;; evaluations one should always bind it to some variable.

;; @@@ Argument list mapping:
;; ==========================
;; Because `defadvice' allows the specification of the argument list of the
;; advised function we need a mapping mechanism that maps this argument list
;; onto that of the original function. For example, somebody might specify
;; `(sym newdef)' as the argument list of `fset', while advice might use
;; `(&rest ad-subr-args)' as the argument list of the original function
;; (depending on what Emacs version is used). Hence SYM and NEWDEF have to
;; be properly mapped onto the &rest variable when the original definition is
;; called. Advice automatically takes care of that mapping, hence, the advice 
;; programmer can specify an argument list without having to know about the
;; exact structure of the original argument list as long as the new argument
;; list takes a compatible number/magnitude of actual arguments.

;; @@@ Definition of subr argument lists:
;; ======================================
;; When advice constructs the advised definition of a function it has to
;; know the argument list of the original function. For functions and macros
;; the argument list can be determined from the actual definition, however,
;; for subrs there is no such direct access available. In Lemacs and for some
;; subrs in Emacs-19 the argument list of a subr can be determined from
;; its documentation string, in a v18 Emacs even that is not possible. If
;; advice cannot at all determine the argument list of a subr it uses
;; `(&rest ad-subr-args)' which will always work but is inefficient because
;; it conses up arguments. The macro `ad-define-subr-args' can be used by
;; the advice programmer to explicitly tell advice about the argument list
;; of a certain subr, for example,
;;
;;    (ad-define-subr-args 'fset '(sym newdef))
;;
;; is used by advice itself to tell a v18 Emacs about the arguments of `fset'.
;; The following can be used to undo such a definition:
;;
;;    (ad-undefine-subr-args 'fset)
;;
;; The argument list definition is stored on the property list of the subr
;; name symbol. When an argument list could be determined from the
;; documentation string it will be cached under that property. The general
;; mechanism for looking up the argument list of a subr is the following:
;; 1) look for a definition stored on the property list
;; 2) if that failed try to infer it from the documentation string and
;;    if successful cache it on the property list
;; 3) otherwise use `(&rest ad-subr-args)'

;; @@ Activation and deactivation:
;; ===============================
;; The definition of an advised function does not change until all its advice
;; gets actually activated. Activation can either happen with the `activate'
;; flag specified in the `defadvice', with an explicit call or interactive
;; invocation of `ad-activate', or if forward advice is enabled (i.e., the
;; value of `ad-activate-on-definition' is t) at the time an already advised
;; function gets defined.

;; When a function gets first activated its original definition gets saved,
;; all defined and enabled pieces of advice will get combined with the
;; original definition, the resulting definition might get compiled depending
;; on some conditions described below, and then the function will get
;; redefined with the advised definition.  This also means that undefined
;; functions cannot get activated even though they might be already advised.

;; The advised definition will get compiled either if `ad-activate' was called
;; interactively with a prefix argument, or called explicitly with its second
;; argument as t, or, if this was a case of forward advice if the original
;; definition of the function was compiled. If the advised definition was
;; constructed during "preactivation" (see below) then that definition will
;; be already compiled because it was constructed during byte-compilation of
;; the file that contained the `defadvice' with the `preactivate' flag.

;; `ad-deactivate' can be used to back-define an advised function to its
;; original definition. It can be called interactively or directly. Because
;; `ad-activate' caches the advised definition the function can be
;; reactivated via `ad-activate' with only minor overhead (it is checked
;; whether the current advice state is consistent with the cached
;; definition, see the section on caching below).

;; `ad-activate-regexp' and `ad-deactivate-regexp' can be used to de/activate
;; all currently advised function that have a piece of advice with a name that
;; contains a match for a regular expression. These functions can be used to
;; de/activate sets of functions depending on certain advice naming
;; conventions.

;; Finally, `ad-activate-all' and `ad-deactivate-all' can be used to
;; de/activate all currently advised functions. These are useful to
;; (temporarily) return to an un/advised state.

;; @@@ Reasons for the separation of advice definition and activation:
;; ===================================================================
;; As already mentioned, advising happens in two stages:

;;   1) definition of various pieces of advice
;;   2) activation of all advice currently defined and enabled

;; The advantage of this is that various pieces of advice can be defined
;; before they get combined into an advised definition which avoids
;; unnecessary constructions of intermediate advised definitions. The more
;; important advantage is that it allows the implementation of forward advice.
;; Advice information for a certain function accumulates as the value of the
;; `advice-info' property of the function symbol. This accumulation is
;; completely independent of the fact that that function might not yet be
;; defined. The special forms `defun' and `defmacro' have been advised to
;; check whether the function/macro they defined had advice information
;; associated with it. If so and forward advice is enabled, the original
;; definition will be saved, and then the advice will be activated. When a
;; file is loaded in a v18 Emacs the functions/macros it defines are also
;; defined with calls to `defun/defmacro'.  Hence, we can forward advise
;; functions/macros which will be defined later during a load/autoload of some
;; file (for compiled files generated by jwz's byte-compiler in a v19 Emacs
;; this is slightly more complicated but the basic idea is the same).

;; @@ Enabling/disabling pieces or sets of advice:
;; ===============================================
;; A major motivation for the development of this advice package was to bring
;; a little bit more structure into the function overloading chaos in Emacs
;; Lisp. Many packages achieve some of their functionality by adding a little
;; bit (or a lot) to the standard functionality of some Emacs Lisp function.
;; ange-ftp is a very popular package that achieves its magic by overloading
;; most Emacs Lisp functions that deal with files. A popular function that's
;; overloaded by many packages is `expand-file-name'. The situation that one
;; function is multiply overloaded can arise easily.

;; Once in a while it would be desirable to be able to disable some/all
;; overloads of a particular package while keeping all the rest.  Ideally -
;; at least in my opinion - these overloads would all be done with advice,
;; I know I am dreaming right now... In that ideal case the enable/disable
;; mechanism of advice could be used to achieve just that.

;; Every piece of advice is associated with an enablement flag. When the
;; advised definition of a particular function gets constructed (e.g., during
;; activation) only the currently enabled pieces of advice will be considered.
;; This mechanism allows one to have different "views" of an advised function
;; dependent on what pieces of advice are currently enabled.

;; Another motivation for this mechanism is that it allows one to define a
;; piece of advice for some function yet keep it dormant until a certain
;; condition is met. Until then activation of the function will not make use
;; of that piece of advice. Once the condition is met the advice can be
;; enabled and a reactivation of the function will add its functionality as
;; part of the new advised definition. For example, the advices of `defun'
;; etc. used by advice itself will stay disabled until `ad-start-advice' is
;; called and some variables have the proper values.  Hence, if somebody
;; else advised these functions too and activates them the advices defined
;; by advice will get used only if they are intended to be used.

;; The main interface to this mechanism are the interactive functions
;; `ad-enable-advice' and `ad-disable-advice'. For example, the following
;; would disable a particular advice of the function `foo':
;;
;;    (ad-disable-advice 'foo 'before 'my-advice)
;;
;; This call by itself only changes the flag, to get the proper effect in
;; the advised definition too one has to activate `foo' with
;;
;;    (ad-activate 'foo)
;;
;; or interactively. To disable whole sets of advices one can use a regular
;; expression mechanism. For example, let us assume that ange-ftp actually
;; used advice to overload all its functions, and that it used the
;; "ange-ftp-" prefix for all its advice names, then we could temporarily
;; disable all its advices with
;;
;;    (ad-disable-regexp "^ange-ftp-")
;;
;; and the following call would put that actually into effect:
;;
;;    (ad-activate-regexp "^ange-ftp-")
;;
;; A saver way would have been to use
;;
;;    (ad-update-regexp "^ange-ftp-")
;;
;; instead which would have only reactivated currently actively advised
;; functions, but not functions that were currently deactivated. All these
;; functions can also be called interactively.

;; A certain piece of advice is considered a match if its name contains a
;; match for the regular expression. To enable ange-ftp again we would use
;; `ad-enable-regexp' and then activate or update again.

;; @@ Forward advice, function definition hooks:
;; =============================================
;; Because most Emacs Lisp packages are loaded on demand via an autoload
;; mechanism it is essential to be able to "forward advise" functions.
;; Otherwise, proper advice definition and activation would make it necessary
;; to preload every file that defines a certain function before it can be
;; advised, which would partly defeat the purpose of the advice mechanism.

;; In the following, "forward advice" always implies its automatic activation
;; once a function gets defined, and not just the accumulation of advice
;; information for a possibly undefined function.

;; Advice implements forward advice mainly via the following: 1) Separation
;; of advice definition and activation that makes it possible to accumulate
;; advice information without having the original function already defined,
;; 2) special versions of the function defining functions `defun', `defmacro'
;; and `fset' that check for advice information whenever they define a
;; function. If advice information was found and forward advice is enabled
;; then the advice will immediately get activated when the function gets
;; defined.

;; @@@ Enabling forward advice:
;; ============================
;; Forward advice is enabled by setting `ad-activate-on-definition' to t
;; and then calling `ad-start-advice' which can either be done interactively,
;; directly with `(ad-start-advice)' in your .emacs, or by setting
;; `ad-start-advice-on-load' to t before advice gets loaded. For example,
;; putting the following into your .emacs will enable forward advice:
;;
;;    (setq ad-start-advice-on-load t)
;;    (setq ad-activate-on-definition t)
;;
;; "Activation on definition" means, that whenever a function gets defined
;; with either `defun', `defmacro', `fset' or by loading a byte-compiled
;; file, and the function has some advice-info stored with it then that
;; advice will get activated right away.

;; If jwz's byte-compiler is used then `ad-use-jwz-byte-compiler' should
;; be t in order to make forward advice work with functions defined in
;; compiled files generated by that compiler. In v19s which use this
;; compiler the value of this variable will be correct automatically.
;; If you use a v18 Emacs in conjunction with jwz's compiler and you want
;; to use forward advice then you should check its value after loading
;; advice. If it is nil set it explicitly with
;;
;;    (setq ad-use-jwz-byte-compiler t)
;;
;; along with `ad-activate-on-definition' before you start advice (see above).

;; IMPORTANT: A v18 Emacs + jwz's compiler + forward advice means performance
;;            tradeoffs which are described below.

;; @@@ Forward advice with compiled files generated by jwz's byte-compiler:
;; ========================================================================
;; The v18 byte-compiler only uses `defun/defmacro' to define compiled
;; functions, hence, providing advised versions of these functions was
;; sufficient to achieve forward advice. With the advent of Jamie Zawinski's
;; optimizing byte-compiler which is now standardly used in Emacs-19 and
;; Lemacs things became more complicated. jwz's compiler defines functions
;; in hunks of byte-code without explicit usage of `defun/defmacro'. To
;; still provide forward advice even in this scenario, advice defines an
;; advised version of the `byte-code' subr that scans its arguments for
;; function definitions during the loading of compiled files. While this is
;; no problem in a v19 Emacs, because it uses a new datatype for compiled
;; code objects and the `byte-code' subr is only rarely used at all, it
;; presents a major problem in a v18 Emacs because there calls to
;; `byte-code' are the only means of executing compiled code (every body of
;; a compiled function contains a call to `byte-code'). Because the advised
;; `byte-code' has to perform some extra checks every call to a compiled
;; function becomes more expensive.

;; Enabling forward advice leads to performance degradation in the following
;; situations:
;; - A v18 Emacs is used and the value of `ad-use-jwz-byte-compiler' is t
;;   (either because jwz's byte-compiler is used instead of the standard v18
;;   compiler, or some compiled files generated by jwz's compiler are used).
;; - A v19 Emacs is used with some old-style v18 compiled files.
;; Some performance experiments I conducted showed that function call intensive
;; code (such as the highly recursive byte-compiler itself) slows down by a 
;; factor of 1.8. Function call intensive code that runs while a file gets
;; loaded can slow down by a factor of 6! For the v19 scenario this performance
;; lossage would only apply to code that was loaded from old v18 compiled
;; files.

;; MORAL: If you use a v18 Emacs in conjunction with jwz's byte-compiler you
;; should think twice whether you really need forward advice. There are some
;; alternatives to forward advice described below that might give you what
;; you need without the loss of performance (that performance loss probably
;; outweighs by far any performance gain due to the optimizing nature of jwz's
;; compiler).

;; @@@ Alternatives to automatic activation of forward advice:
;; ===========================================================
;; If you use a v18 Emacs in conjunction with jwz's compiler, or you simply
;; don't trust the automatic activation mechanism of forward advice, then
;; you can use some of the following alternatives to get around that:
;; - Preload the file that contains the definition of the function that you
;;   want to advice. Inelegant and wasteful, but it works.
;; - If the package that contains the definition of the function you want to
;;   advise has any mode hooks, and the advised function is only used once such
;;   a mode has been entered, then you can activate the advice in the mode 
;;   hook. Just put a form like `(ad-activate 'my-advised-fn t)' into the
;;   hook definition. The caching mechanism will reuse advised definitions,
;;   so calling that mode hook over and over again will not construct
;;   advised definitions over and over again, so you won't loose any
;;   performance.
;; - If your Emacs comes with file load hooks (such as v19's
;;   `after-load-alist' mechanism), then you can put the activation form
;;   into that, for example, add `("myfile" (ad-activate 'my-advised-fn t))'
;;   to it to activate the advice right ater "myfile" got loaded.

;; @@@ Function definition hooks:
;; ==============================
;; Automatic activation of forward advice is implemented as an application
;; of a more general function definition hook mechanism. After a function
;; gets re/defined with `defun/defmacro/fset' or via a hunk of byte-code
;; during the loading of a byte-compiled file, and function definition hooks
;; are enabled, then all hook functions stored in `ad-definition-hooks' are
;; run with the variable `ad-defined-function' bound to the name of the 
;; currently defined function.

;; Function definition hooks can be enabled with
;;
;;    (setq ad-enable-definition-hooks t)
;;
;; before advice gets started with `ad-start-advice'. Setting 
;; `ad-activate-on-definition' to t automatically enables definition hooks
;; regardless of the value of `ad-enable-definition-hooks'.

;; @@@ Wish list:
;; ==============
;; - The implementation of definition hooks for v19 compiled files would be
;;   safer if jwz's byte-compiler used something like `byte-code-tl' instead
;;   of `byte-code' to execute hunks of function defining byte-code at the
;;   top level of compiled files.
;; - Definition hooks should be implemented directly as part of the C-code
;;   that implements `fset', because then Advice wouldn't have to use all
;;   these dirty hacks to achieve this functionality.

;; @@ Caching of advised definitions:
;; ==================================
;; After an advised definition got constructed it gets cached as part of the
;; advised function's advice-info so it can be reused, for example, after an
;; intermediate deactivation. Because the advice-info of a function might
;; change between the time of caching and reuse a cached definition gets
;; a cache-id associated with it so it can be verified whether the cached
;; definition is still valid (the main application of this is preactivation
;; - see below).

;; When an advised function gets activated and a verifiable cached definition
;; is available, then that definition will be used instead of creating a new
;; advised definition from scratch. If you want to make sure that a new
;; definition gets constructed then you should use `ad-clear-cache' before you
;; activate the advised function.

;; @@ Preactivation:
;; =================
;; Constructing an advised definition is moderately expensive. In a situation
;; where one package defines a lot of advised functions it might be
;; prohibitively expensive to do all the advised definition construction at
;; runtime. Preactivation is a mechanism that allows compile-time construction
;; of compiled advised definitions that can be activated cheaply during
;; runtime. Preactivation uses the caching mechanism to do that. Here's how it
;; works:

;; When the byte-compiler compiles a `defadvice' that has the `preactivate'
;; flag specified, it uses the current original definition of the advised
;; function plus the advice specified in this `defadvice' (even if it is
;; specified as disabled) and all other currently enabled pieces of advice to
;; construct an advised definition and an identifying cache-id and makes them
;; part of the `defadvice' expansion which will then be compiled by the
;; byte-compiler (to ensure that in a v18 emacs you have to put the
;; `defadvice' inside a `defun' to get it compiled and then you have to call
;; that compiled `defun' in order to actually execute the `defadvice'). When
;; the file with the compiled, preactivating `defadvice' gets loaded the
;; precompiled advised definition will be cached on the advised function's
;; advice-info. When it gets activated (can be immediately on execution of the
;; `defadvice' or any time later) the cache-id gets checked against the
;; current state of advice and if it is verified the precompiled definition
;; will be used directly (the verification is pretty cheap). If it couldn't get
;; verified a new advised definition for that function will be built from
;; scratch, hence, the efficiency added by the preactivation mechanism does
;; not at all impair the flexibility of the advice mechanism.

;; MORAL: In order get all the efficiency out of preactivation the advice
;;        state of an advised function at the time the file with the
;;        preactivating `defadvice' gets byte-compiled should be exactly
;;        the same as it will be when the advice of that function gets
;;        actually activated. If it is not there is a high chance that the
;;        cache-id will not match and hence a new advised definition will
;;        have to be constructed at runtime.

;; Preactivation and forward advice do not contradict each other. It is
;; perfectly ok to load a file with a preactivating `defadvice' before the
;; original definition of the advised function is available. The constructed
;; advised definition will be used once the original function gets defined and
;; its advice gets activated. The only constraint is that at the time the
;; file with the preactivating `defadvice' got compiled the original function
;; definition was available.

;; TIPS: Here are some indications that a preactivation did not work the way
;;       you intended it to work:
;;       - Activation of the advised function takes longer than usual/expected
;;       - The byte-compiler gets loaded while an advised function gets
;;         activated
;;       - `byte-compile' is part of the `features' variable even though you
;;         did not use the byte-compiler
;;       Right now advice does not provide an elegant way to find out whether
;;       and why a preactivation failed. What you can do is to trace the
;;       function `ad-cache-id-verification-code' (with the function
;;       `trace-function-background' defined in my trace.el package) before
;;       any of your advised functions get activated. After they got
;;       activated check whether all calls to `ad-cache-id-verification-code'
;;       returned `verified' as a result. Other values indicate why the
;;       verification failed which should give you enough information to
;;       fix your preactivation/compile/load/activation sequence.

;; IMPORTANT: There is one case (that I am aware of) that can make 
;; preactivation fail, i.e., a preconstructed advised definition that does
;; NOT match the current state of advice gets used nevertheless. That case
;; arises if one package defines a certain piece of advice which gets used
;; during preactivation, and another package incompatibly redefines that 
;; very advice (i.e., same function/class/name), and it is the second advice
;; that is available when the preconstructed definition gets activated, and
;; that was the only definition of that advice so far (`ad-add-advice' 
;; catches advice redefinitions and clears the cache in such a case). 
;; Catching that would make the cache verification too expensive.

;; MORAL-II: Redefining somebody else's advice is BAAAAD (to speak with
;; George Walker Bush), and why would you redefine your own advice anyway?
;; Advice is a mechanism to facilitate function redefinition, not advice
;; redefinition (wait until I write Meta-Advice :-). If you really have
;; to undo somebody else's advice try to write a "neutralizing" advice.

;; @@ Advising macros and special forms and other dangerous things:
;; ================================================================
;; Look at the corresponding tutorial sections for more information on
;; these topics. Here it suffices to point out that the special treatment
;; of macros and special forms by the byte-compiler can lead to problems
;; when they get advised. Macros can create problems because they get
;; expanded at compile time, hence, they might not have all the necessary
;; runtime support and such advice cannot be de/activated or changed as
;; it is possible for functions. Special forms create problems because they
;; have to be advised "into" macros, i.e., an advised special form is a
;; implemented as a macro, hence, in most cases the byte-compiler will
;; not recognize it as a special form anymore which can lead to very strange
;; results.
;;
;; MORAL: - Only advise macros or special forms when you are absolutely sure
;;          what you are doing.
;;        - As a safety measure, always do `ad-deactivate-all' before you
;;          byte-compile a file to make sure that even if some inconsiderate
;;          person advised some special forms you'll get proper compilation
;;          results. After compilation do `ad-activate-all' to get back to
;;          the previous state.

;; @@ Adding a piece of advice with `ad-add-advice':
;; =================================================
;; The non-interactive function `ad-add-advice' can be used to add a piece of
;; advice to some function without using `defadvice'. This is useful if advice
;; has to be added somewhere by a function (also look at `ad-make-advice').

;; @@ Activation/deactivation advices, file load hooks:
;; ====================================================
;; There are two special classes of advice called `activation' and
;; `deactivation'. The body forms of these advices are not included into the
;; advised definition of a function, rather they are assembled into a hook
;; form which will be evaluated whenever the advice-info of the advised
;; function gets activated or deactivated. One application of this mechanism
;; is to define file load hooks for files that do not provide such hooks
;; (v19s already come with a general file-load-hook mechanism, v18s don't).
;; For example, suppose you want to print a message whenever `file-x' gets
;; loaded, and suppose the last function defined in `file-x' is
;; `file-x-last-fn'.  Then we can define the following advice:
;;
;;   (defadvice file-x-last-fn (activation file-x-load-hook)
;;      "Executed whenever file-x is loaded"
;;      (if load-in-progress (message "Loaded file-x")))
;;
;; This will constitute a forward advice for function `file-x-last-fn' which
;; will get activated when `file-x' is loaded (only if forward advice is
;; enabled of course). Because there are no "real" pieces of advice
;; available for it, its definition will not be changed, but the activation
;; advice will be run during its activation which is equivalent to having a
;; file load hook for `file-x'.

;; @@ Summary of main advice concepts:
;; ===================================
;; - Definition:
;;     A piece of advice gets defined with `defadvice' and added to the
;;     `advice-info' property of a function.
;; - Enablement:
;;     Every piece of advice has an enablement flag associated with it. Only
;;     enabled advices are considered during construction of an advised
;;     definition.
;; - Activation:
;;     Redefine an advised function with its advised definition. Constructs
;;     an advised definition from scratch if no verifiable cached advised
;;     definition is available and caches it.
;; - Deactivation:
;;     Back-define an advised function to its original definition.
;; - Update:
;;     Reactivate an advised function but only if its advice is currently 
;;     active. This can be used to bring all currently advised function up
;;     to date with the current state of advice without also activating
;;     currently deactivated functions.
;; - Caching:
;;     Is the saving of an advised definition and an identifying cache-id so
;;     it can be reused, for example, for activation after deactivation.
;; - Preactivation:
;;     Is the construction of an advised definition according to the current
;;     state of advice during byte-compilation of a file with a preactivating
;;     `defadvice'. That advised definition can then rather cheaply be used
;;     during activation without having to construct an advised definition
;;     from scratch at runtime.

;; @@ Summary of interactive advice manipulation functions:
;; ========================================================
;; The following interactive functions can be used to manipulate the state
;; of advised functions (all of them support completion on function names,
;; advice classes and advice names):

;; - ad-activate to activate the advice of a FUNCTION
;; - ad-deactivate to deactivate the advice of a FUNCTION
;; - ad-update   to activate the advice of a FUNCTION unless it was not
;;               yet activated or is currently deactivated.
;; - ad-unadvise deactivates a FUNCTION and removes all of its advice 
;;               information, hence, it cannot be activated again
;; - ad-recover  tries to redefine a FUNCTION to its original definition and
;;               discards all advice information (a low-level `ad-unadvise').
;;               Use only in emergencies.

;; - ad-remove-advice removes a particular piece of advice of a FUNCTION.
;;               You still have to do call `ad-activate' or `ad-update' to
;;               activate the new state of advice.
;; - ad-enable-advice enables a particular piece of advice of a FUNCTION.
;; - ad-disable-advice disables a particular piece of advice of a FUNCTION.
;; - ad-enable-regexp maps over all currently advised functions and enables
;;               every advice whose name contains a match for a regular
;;               expression.
;; - ad-disable-regexp disables matching advices.

;; - ad-activate-regexp   activates all advised function with a matching advice
;; - ad-deactivate-regexp deactivates all advised function with matching advice
;; - ad-update-regexp     updates all advised function with a matching advice
;; - ad-activate-all      activates all advised functions
;; - ad-deactivate-all    deactivates all advised functions
;; - ad-update-all        updates all advised functions
;; - ad-unadvise-all      unadvises all advised functions
;; - ad-recover-all       recovers all advised functions

;; - ad-compile byte-compiles a function/macro if it is compilable.

;; @@ Summary of forms with special meanings when used within an advice:
;; =====================================================================
;;   ad-return-value   name of the return value variable (get/settable)
;;   ad-subr-args      name of &rest argument variable used for advised
;;                     subrs whose actual argument list cannot be
;;                     determined (get/settable)
;;   (ad-get-arg <pos>), (ad-get-args <pos>),
;;   (ad-set-arg <pos> <value>), (ad-set-args <pos> <value-list>)
;;                     argument access text macros to get/set the values of
;;                     actual arguments at a certain position
;;   ad-arg-bindings   text macro that returns the actual names, values
;;                     and types of the arguments as a list of bindings. The
;;                     order of the bindings corresponds to the order of the
;;                     arguments. The individual fields of every binding (name,
;;                     value and type) can be accessed with the function
;;                     `ad-arg-binding-field' (see example above).
;;   ad-do-it          text macro that identifies the place where the original
;;                     or wrapped definition should go in an around advice


;; @ Foo games: An advice tutorial
;; ===============================
;; The following tutorial was created in Emacs 18.59. Left-justified
;; s-expressions are input forms followed by one or more result forms.
;; First we have to start the advice magic:
;;
;; (ad-start-advice)
;; nil
;;
;; We start by defining an innocent looking function `foo' that simply
;; adds 1 to its argument X:
;;  
;; (defun foo (x)
;;   "Add 1 to X."
;;   (1+ x))
;; foo
;;
;; (foo 3)
;; 4
;;
;; @@ Defining a simple piece of advice:
;; =====================================
;; Now let's define the first piece of advice for `foo'.  To do that we
;; use the macro `defadvice' which takes a function name, a list of advice
;; specifiers and a list of body forms as arguments.  The first element of
;; the advice specifiers is the class of the advice, the second is its name,
;; the third its position and the rest are some flags. The class of our
;; first advice is `before', its name is `fg-add2', its position among the
;; currently defined before advices (none so far) is `first', and the advice
;; will be `activate'ed immediately. Advice names are global symbols, hence,
;; the name space conventions used for function names should be applied. All
;; advice names in this tutorial will be prefixed with `fg' for `Foo Games'
;; (because everybody has the right to be inconsistent all the function names
;; used in this tutorial do NOT follow this convention).
;;
;; In the body of an advice we can refer to the argument variables of the
;; original function by name. Here we add 1 to X so the effect of calling
;; `foo' will be to actually add 2. All of the advice definitions below only
;; have one body form for simplicity, but there is no restriction to that
;; extent. Every piece of advice can have a documentation string which will
;; be combined with the documentation of the original function.
;;
;; (defadvice foo (before fg-add2 first activate)
;;   "Add 2 to X."
;;   (setq x (1+ x)))
;; foo
;;
;; (foo 3)
;; 5
;;
;; @@ Specifying the position of an advice:
;; ========================================
;; Now we define the second before advice which will cancel the effect of
;; the previous advice. This time we specify the position as 0 which is
;; equivalent to `first'. A number can be used to specify the zero-based
;; position of an advice among the list of advices in the same class. This
;; time we already have one before advice hence the position specification
;; actually has an effect. So, after the following definition the position
;; of the previous advice will be 1 even though we specified it with `first'
;; above, the reason for this is that the position argument is relative to
;; the currently defined pieces of advice which by now has changed.
;;
;; (defadvice foo (before fg-cancel-add2 0 activate)
;;   "Again only add 1 to X."
;;   (setq x (1- x)))
;; foo
;;
;; (foo 3)
;; 4
;;
;; @@ Redefining a piece of advice:
;; ================================
;; Now we define an advice with the same class and same name but with a
;; different position. Defining an advice in a class in which an advice with
;; that name already exists is interpreted as a redefinition of that
;; particular advice, in which case the position argument will be ignored
;; and the previous position of the redefined piece of advice is used.
;; Advice flags can be specified with non-ambiguous initial substrings, hence,
;; from now on we'll use `act' instead of the verbose `activate'.
;;
;; (defadvice foo (before fg-cancel-add2 last act)
;;   "Again only add 1 to X."
;;   (setq x (1- x)))
;; foo
;;
;; @@ Assembly of advised documentation:
;; =====================================
;; The documentation strings of the various pieces of advice are assembled
;; in order which shows that advice `fg-cancel-add2' is still the first
;; `before' advice even though we specified position `last' above:
;;
;; (documentation 'foo)
;; "Add 1 to X.
;;
;; This function is advised with the following advice(s):
;;
;; fg-cancel-add2 (before):
;; Again only add 1 to X.
;;
;; fg-add2 (before):
;; Add 2 to X."
;;
;; @@ Advising interactive behavior:
;; =================================
;; We can make a function interactive (or change its interactive behavior)
;; by specifying an interactive form in one of the before or around
;; advices (there could also be body forms in this advice). The particular
;; definition always assigns 5 as an argument to X which gives us 6 as a
;; result when we call foo interactively:
;;
;; (defadvice foo (before fg-inter last act)
;;   "Use 5 as argument when called interactively."
;;   (interactive (list 5)))
;; foo
;;
;; (call-interactively 'foo)
;; 6
;;
;; If more than one advice have an interactive declaration, then the one of
;; the advice with the smallest position will be used (before advices go
;; before around and after advices), hence, the declaration below does
;; not have any effect:
;;
;; (defadvice foo (before fg-inter2 last act)
;;   (interactive (list 6)))
;; foo
;;
;; (call-interactively 'foo)
;; 6
;;
;; Let's have a look at what the definition of `foo' looks like now 
;; (indentation added by hand for legibility):
;;
;; (symbol-function 'foo)
;; (lambda (x)
;;   "$ad-doc: foo$"
;;   (interactive (list 5))
;;   (let (ad-return-value) 
;;     (setq x (1- x)) 
;;     (setq x (1+ x)) 
;;     (setq ad-return-value (ad-Orig-foo x)) 
;;     ad-return-value))
;;
;; @@ Around advices:
;; ==================
;; Now we'll try some `around' advices. An around advice is a wrapper around
;; the original definition. It can shadow or establish bindings for the
;; original definition, and it can look at and manipulate the value returned
;; by the original function. The position of the special keyword `ad-do-it'
;; specifies where the code of the original function will be executed. The
;; keyword can appear multiple times which will result in multiple calls of
;; the original function in the resulting advised code. Note, that if we don't
;; specify a position argument (i.e., `first', `last' or a number), then 
;; `first' (or 0) is the default):
;;
;; (defadvice foo (around fg-times-2 act)
;;   "First double X."
;;   (let ((x (* x 2)))
;;     ad-do-it))
;; foo
;;
;; (foo 3)
;; 7
;;
;; Around advices are assembled like onion skins where the around advice
;; with position 0 is the outermost skin and the advice at the last position
;; is the innermost skin which is directly wrapped around the call of the
;; original definition of the function. Hence, after the next `defadvice' we
;; will first multiply X by 2 then add 1 and then call the original
;; definition (i.e., add 1 again):
;;
;; (defadvice foo (around fg-add-1 last act)
;;   "Add 1 to X."
;;   (let ((x (1+ x)))
;;     ad-do-it))
;; foo
;;
;; (foo 3)
;; 8
;;
;; Again, let's see what the definition of `foo' looks like so far:
;;
;; (symbol-function 'foo)
;; (lambda (x) 
;;   "$ad-doc: foo$"
;;   (interactive (list 5)) 
;;   (let (ad-return-value) 
;;     (setq x (1- x)) 
;;     (setq x (1+ x)) 
;;     (let ((x (* x 2))) 
;;       (let ((x (1+ x))) 
;;         (setq ad-return-value (ad-Orig-foo x)))) 
;;     ad-return-value))
;;
;; @@ Controlling advice activation:
;; =================================
;; In every `defadvice' so far we have used the flag `activate' to activate
;; the advice immediately after its definition, and that's what we want in
;; most cases. However, if we define multiple pieces of advice for a single
;; function then activating every advice immediately is inefficient. A
;; better way to do this is to only activate the last defined advice.
;; For example:
;;
;; (defadvice foo (after fg-times-x)
;;   "Multiply the result with X."
;;   (setq ad-return-value (* ad-return-value x)))
;; foo
;;
;; This still yields the same result as before:
;; (foo 3)
;; 8
;;
;; Now we define another advice and activate which will also activate the
;; previous advice `fg-times-x'. Note the use of the special variable
;; `ad-return-value' in the body of the advice which is set to the result of
;; the original function. If we change its value then the value returned by
;; the advised function will be changed accordingly:
;;
;; (defadvice foo (after fg-times-x-again act)
;;   "Again multiply the result with X."
;;   (setq ad-return-value (* ad-return-value x)))
;; foo
;;
;; Now the advices have an effect:
;;
;; (foo 3)
;; 72
;;
;; @@ Protecting advice execution:
;; ===============================
;; Once in a while we define an advice to perform some cleanup action, 
;; for example:
;;
;; (defadvice foo (after fg-cleanup last act)
;;   "Do some cleanup."
;;   (print "Let's clean up now!"))
;; foo
;;
;; However, in case of an error the cleanup won't be performed:
;;
;; (condition-case error
;;     (foo t)
;;   (error 'error-in-foo))
;; error-in-foo
;;
;; To make sure a certain piece of advice gets executed even if some error or
;; non-local exit occurred in any preceding code, we can protect it by using
;; the `protect' keyword. (if any of the around advices is protected then the
;; whole around advice onion will be protected):
;;
;; (defadvice foo (after fg-cleanup prot act)
;;   "Do some protected cleanup."
;;   (print "Let's clean up now!"))
;; foo
;;
;; Now the cleanup form will be executed even in case of an error:
;;
;; (condition-case error
;;     (foo t)
;;   (error 'error-in-foo))
;; "Let's clean up now!"
;; error-in-foo
;;
;; Again, let's see what `foo' looks like:
;;
;; (symbol-function 'foo)
;; (lambda (x) 
;;   "$ad-doc: foo$"
;;   (interactive (list 5)) 
;;   (let (ad-return-value) 
;;     (unwind-protect 
;;         (progn (setq x (1- x)) 
;;                (setq x (1+ x)) 
;;                (let ((x (* x 2))) 
;;                  (let ((x (1+ x))) 
;;                    (setq ad-return-value (ad-Orig-foo x)))) 
;;                (setq ad-return-value (* ad-return-value x)) 
;;                (setq ad-return-value (* ad-return-value x))) 
;;       (print "Let's clean up now!")) 
;;     ad-return-value))
;;
;; @@ Compilation of advised definitions:
;; ======================================
;; Finally, we can specify the `compile' keyword in a `defadvice' to say
;; that we want the resulting advised function to be byte-compiled
;; (`compile' will be ignored unless we also specified `activate'):
;;
;; (defadvice foo (after fg-cleanup prot act comp)
;;   "Do some protected cleanup."
;;   (print "Let's clean up now!"))
;; foo
;;
;; Now `foo' is byte-compiled:
;;
;; (symbol-function 'foo)
;; (lambda (x) 
;;   "$ad-doc: foo$"
;;   (interactive (byte-code "....." [5] 1)) 
;;   (byte-code "....." [ad-return-value x nil ((byte-code "....." [print "Let's clean up now!"] 2)) * 2 ad-Orig-foo] 6))
;;
;; (foo 3)
;; "Let's clean up now!"
;; 72
;;
;; @@ Enabling and disabling pieces of advice:
;; ===========================================
;; Once in a while it is desirable to temporarily disable a piece of advice
;; so that it won't be considered during activation, for example, if two
;; different packages advise the same function and one wants to temporarily
;; neutralize the effect of the advice of one of the packages.
;;
;; The following disables the after advice `fg-times-x' in the function `foo'.
;; All that does is to change a flag for this particular advice. All the
;; other information defining it will be left unchanged (e.g., its relative
;; position in this advice class, etc.).
;;
;; (ad-disable-advice 'foo 'after 'fg-times-x)
;; nil
;;
;; For this to have an effect we have to activate `foo':
;;
;; (ad-activate 'foo)
;; foo
;;
;; (foo 3)
;; "Let's clean up now!"
;; 24
;;
;; If we want to disable all multiplication advices in `foo' we can use a
;; regular expression that matches the names of such advices. Actually, any
;; advice name that contains a match for the regular expression will be
;; called a match. A special advice class `any' can be used to consider
;; all advice classes:
;;
;; (ad-disable-advice 'foo 'any "^fg-.*times")
;; nil
;;
;; (ad-activate 'foo)
;; foo
;;
;; (foo 3)
;; "Let's clean up now!"
;; 5
;;
;; To enable the disabled advice we could use either `ad-enable-advice'
;; similar to `ad-disable-advice', or as an alternative `ad-enable-regexp'
;; which will enable matching advices in ALL currently advised functions.
;; Hence, this can be used to dis/enable advices made by a particular
;; package to a set of functions as long as that package obeys standard
;; advice name conventions.  We prefixed all advice names with `fg-', hence
;; the following will do the trick (`ad-enable-regexp' returns the number
;; of matched advices):
;;
;; (ad-enable-regexp "^fg-")
;; 9
;;
;; The following will activate all currently active advised functions that
;; contain some advice matched by the regular expression. This is a save
;; way to update the activation of advised functions whose advice changed
;; in some way or other without accidentally also activating currently
;; deactivated functions:
;;
;; (ad-update-regexp "^fg-")
;; nil
;;
;; (foo 3)
;; "Let's clean up now!"
;; 72
;;
;; Another use for the dis/enablement mechanism is to define a piece of advice
;; and keep it "dormant" until a particular condition is satisfied, i.e., until
;; then the advice will not be used during activation. The `disable' flag lets
;; one do that with `defadvice':
;;
;; (defadvice foo (before fg-1-more dis)
;;   "Add yet 1 more."
;;   (setq x (1+ x)))
;; foo
;;
;; (ad-activate 'foo)
;; foo
;;
;; (foo 3)
;; "Let's clean up now!"
;; 72
;;
;; (ad-enable-advice 'foo 'before 'fg-1-more)
;; nil
;;
;; (ad-activate 'foo)
;; foo
;;
;; (foo 3)
;; "Let's clean up now!"
;; 160
;;
;; @@ Caching:
;; ===========
;; Advised definitions get cached to allow efficient activation/deactivation
;; without having to reconstruct them if nothing in the advice-info of a
;; function has changed. The following idiom can be used to temporarily
;; deactivate functions that have a piece of advice defined by a certain
;; package (we save the old definition to check out caching):
;;
;; (setq old-definition (symbol-function 'foo))
;; (lambda (x) ....)
;;
;; (ad-deactivate-regexp "^fg-")
;; nil
;;
;; (foo 3)
;; 4
;;
;; (ad-activate-regexp "^fg-")
;; nil
;;
;; (eq old-definition (symbol-function 'foo))
;; t
;;
;; (foo 3)
;; "Let's clean up now!"
;; 160
;;
;; @@ Forward advice:
;; ==================
;; To enable automatic activation of forward advice we first have to set
;; `ad-activate-on-definition' to t and restart advice:
;;
;; (setq ad-activate-on-definition t)
;; t
;;
;; (ad-start-advice)
;; (ad-activate-defined-function)
;;
;; Let's define a piece of advice for an undefined function:
;;
;; (defadvice bar (before fg-sub-1-more act)
;;   "Subtract one more from X."
;;   (setq x (1- x)))
;; bar
;;
;; `bar' is not yet defined:
;; (fboundp 'bar)
;; nil
;;
;; Now we define it and the forward advice will get activated (only because
;; `ad-activate-on-definition' was t when we started advice above with
;; `ad-start-advice'):
;;
;; (defun bar (x)
;;   "Subtract 1 from X."
;;   (1- x))
;; bar
;;
;; (bar 4)
;; 2
;;
;; Redefinition will activate any available advice if the value of
;; `ad-redefinition-action' is either `warn', `accept' or `discard':
;;
;; (defun bar (x)
;;   "Subtract 2 from X."
;;   (- x 2))
;; bar
;;
;; (bar 4)
;; 1
;;
;; @@ Preactivation:
;; =================
;; Constructing advised definitions is moderately expensive, hence, it is
;; desirable to have a way to construct them at byte-compile time.
;; Preactivation is a mechanism that allows one to do that.
;;
;; (defun fie (x)
;;   "Multiply X by 2."
;;   (* x 2))
;; fie
;;
;; (defadvice fie (before fg-times-4 preact)
;;   "Multiply X by 4."
;;   (setq x (* x 2)))
;; fie
;;
;; This advice did not affect `fie'...
;;
;; (fie 2)
;; 4
;;
;; ...but it constructed a cached definition that will be used once `fie' gets
;; activated as long as its current advice state is the same as it was during
;; preactivation:
;;
;; (setq cached-definition (ad-get-cache-definition 'fie))
;; (lambda (x) ....)
;;
;; (ad-activate 'fie)
;; fie
;;
;; (eq cached-definition (symbol-function 'fie))
;; t
;;
;; (fie 2)
;; 8
;;
;; If you put a preactivating `defadvice' into an elisp file that gets byte-
;; compiled then the constructed advised definition will get compiled by
;; the byte-compiler. For that to occur in a v18 emacs you have to put the
;; `defadvice' inside a `defun' because the v18 compiler does not compile
;; top-level forms other than `defun' or `defmacro', for example,
;;
;; (defun fg-defadvice-fum ()
;;   (defadvice fum (before fg-times-4 preact act)
;;     "Multiply X by 4."
;;     (setq x (* x 2))))
;; fg-defadvice-fum
;;
;; So far, no `defadvice' for `fum' got executed, but when we compile
;; `fg-defadvice-fum' the `defadvice' will be expanded by the byte compiler.
;; In order for preactivation to be effective we have to have a proper
;; definition of `fum' around at preactivation time, hence, we define it now:
;;
;; (defun fum (x)
;;   "Multiply X by 2."
;;   (* x 2))
;; fum
;;
;; Now we compile the defining function which will construct an advised
;; definition during expansion of the `defadvice', compile it and store it
;; as part of the compiled `fg-defadvice-fum':
;;
;; (ad-compile-function 'fg-defadvice-fum)
;; (lambda nil (byte-code ...))
;;
;; `fum' is still completely unaffected:
;;
;; (fum 2)
;; 4
;;
;; (ad-get-advice-info 'fum)
;; nil
;;
;; (fg-defadvice-fum)
;; fum
;;
;; Now the advised version of `fum' is compiled because the compiled definition
;; constructed during preactivation was used, even though we did not specify
;; the `compile' flag:
;;
;; (symbol-function 'fum)
;; (lambda (x) 
;;   "$ad-doc: fum$"
;;   (byte-code "....." [ad-return-value x nil * 2 ad-Orig-fum] 4))
;;
;; (fum 2)
;; 8
;;
;; A preactivated definition will only be used if it matches the current
;; function definition and advice information. If it does not match it
;; will simply be discarded and a new advised definition will be constructed
;; from scratch. For example, let's first remove all advice-info for `fum':
;;
;; (ad-unadvise 'fum)
;; (("fie") ("bar") ("foo") ...)
;;
;; And now define a new piece of advice:
;;
;; (defadvice fum (before fg-interactive act)
;;   "Make fum interactive."
;;   (interactive "nEnter x: "))
;; fum
;;
;; When we now try to use a preactivation it will not be used because the
;; current advice state is different from the one at preactivation time. This
;; is no tragedy, everything will work as expected just not as efficient,
;; because a new advised definition has to be constructed from scratch:
;;
;; (fg-defadvice-fum)
;; fum
;;
;; A new uncompiled advised definition got constructed:
;;
;; (ad-compiled-p (symbol-function 'fum))
;; nil
;;
;; (fum 2)
;; 8
;;
;; MORAL: To get all the efficiency out of preactivation the function
;; definition and advice state at preactivation time must be the same as the
;; state at activation time. Preactivation does work with forward advice, all
;; that's necessary is that the definition of the forward advised function is
;; available when the `defadvice' with the preactivation gets compiled.
;;
;; @@ Portable argument access:
;; ============================
;; So far, we always used the actual argument variable names to access an
;; argument in a piece of advice. For many advice applications this is
;; perfectly ok and keeps advices simple. However, it decreases portability
;; of advices because it assumes specific argument variable names. For example,
;; if one advises a subr such as `eval-region' which then gets redefined by
;; some package (e.g., edebug) into a function with different argument names,
;; then a piece of advice written for `eval-region' that was written with
;; the subr arguments in mind will break. Similar situations arise when one
;; switches between major Emacs versions, e.g., certain subrs in v18 are
;; functions in v19 and vice versa. Also, in v19s subr argument lists
;; are available and will be used, while they are not available in v18.
;;
;; Argument access text macros allow one to access arguments of an advised
;; function in a portable way without having to worry about all these
;; possibilities. These macros will be translated into the proper access forms
;; at activation time, hence, argument access will be as efficient as if
;; the arguments had been used directly in the definition of the advice.
;;
;; (defun fuu (x y z)
;;   "Add 3 numbers."
;;   (+ x y z))
;; fuu
;;
;; (fuu 1 1 1)
;; 3
;;
;; Argument access macros specify actual arguments at a certain position.
;; Position 0 access the first actual argument, position 1 the second etc.
;; For example, the following advice adds 1 to each of the 3 arguments:
;;
;; (defadvice fuu (before fg-add-1-to-all act)
;;   "Adds 1 to all arguments."
;;   (ad-set-arg 0 (1+ (ad-get-arg 0)))
;;   (ad-set-arg 1 (1+ (ad-get-arg 1)))
;;   (ad-set-arg 2 (1+ (ad-get-arg 2))))
;; fuu
;;
;; (fuu 1 1 1)
;; 6
;;
;; Now suppose somebody redefines `fuu' with a rest argument. Our advice
;; will still work because we used access macros (note, that automatic
;; advice activation is still in effect, hence, the redefinition of `fuu'
;; will automatically activate all its advice):
;;
;; (defun fuu (&rest numbers)
;;   "Add NUMBERS."
;;   (apply '+ numbers))
;; fuu
;;
;; (fuu 1 1 1)
;; 6
;;
;; (fuu 1 1 1 1 1 1)
;; 9
;;
;; What's important to notice is that argument access macros access actual
;; arguments regardless of how they got distributed onto argument variables.
;; In Emacs Lisp the semantics of an actual argument is determined purely
;; by position, hence, as long as nobody changes the semantics of what a
;; certain actual argument at a certain position means the access macros
;; will do the right thing.
;;
;; Because of &rest arguments we need a second kind of access macro that
;; can access all actual arguments starting from a certain position:
;;
;; (defadvice fuu (before fg-print-args act)
;;   "Print all arguments."
;;   (print (ad-get-args 0)))
;; fuu
;;
;; (fuu 1 2 3 4 5)
;; (1 2 3 4 5)
;; 18
;;
;; (defadvice fuu (before fg-set-args act)
;;   "Swaps 2nd and 3rd arg and discards all the rest."
;;   (ad-set-args 1 (list (ad-get-arg 2) (ad-get-arg 1))))
;; fuu
;;
;; (fuu 1 2 3 4 4 4 4 4 4)
;; (1 3 2)
;; 9
;;
;; (defun fuu (x y z)
;;   "Add 3 numbers."
;;   (+ x y z))
;;
;; (fuu 1 2 3)
;; (1 3 2)
;; 9
;;
;; @@ Defining the argument list of an advised function:
;; =====================================================
;; Once in a while it might be desirable to advise a function and additionally
;; give it an extra argument that controls the advised code, for example, one
;; might want to make an interactive function sensitive to a prefix argument.
;; For such cases `defadvice' allows the specification of an argument list
;; for the advised function. Similar to the redefinition of interactive 
;; behavior, the first argument list specification found in the list of before/
;; around/after advices will be used. Of course, the specified argument list
;; should be downward compatible with the original argument list, otherwise
;; functions that call the advised function with the original argument list
;; in mind will break.
;;
;; (defun fii (x)
;;   "Add 1 to X."
;;   (1+ x))
;; fii
;;
;; Now we advise `fii' to use an optional second argument that controls the
;; amount of incrementation. A list following the (optional) position
;; argument of the advice will be interpreted as an argument list
;; specification. This means you cannot specify an empty argument list, and
;; why would you want to anyway?
;;
;; (defadvice fii (before fg-inc-x (x &optional incr) act)
;;   "Increment X by INCR (default is 1)."
;;   (setq x (+ x (1- (or incr 1)))))
;; fii
;;
;; (fii 3)
;; 4
;;
;; (fii 3 2)
;; 5
;;
;; @@ Specifying argument lists of subrs:
;; ======================================
;; The argument lists of subrs cannot be determined directly from Lisp.
;; This means that Advice has to use `(&rest ad-subr-args)' as the
;; argument list of the advised subr which is not very efficient. In Lemacs
;; subr argument lists can be determined from their documentation string, in
;; Emacs-19 this is the case for some but not all subrs. To accommodate
;; for the cases where the argument lists cannot be determined (e.g., in a
;; v18 Emacs) Advice comes with a specification mechanism that allows the
;; advice programmer to tell advice what the argument list of a certain subr
;; really is.
;;
;; In a v18 Emacs the following will return the &rest idiom:
;;
;; (ad-arglist (symbol-function 'car))
;; (&rest ad-subr-args)
;;
;; To tell advice what the argument list of `car' really is we
;; can do the following:
;;
;; (ad-define-subr-args 'car '(list))
;; ((list))
;;
;; Now `ad-arglist' will return the proper argument list (this method is
;; actually used by advice itself for the advised definition of `fset'):
;;
;; (ad-arglist (symbol-function 'car))
;; (list)
;;
;; The defined argument list will be stored on the property list of the
;; subr name symbol. When advice looks for a subr argument list it first
;; checks for a definition on the property list, if that fails it tries
;; to infer it from the documentation string and caches it on the property
;; list if it was successful, otherwise `(&rest ad-subr-args)' will be used.
;;
;; @@ Advising interactive subrs:
;; ==============================
;; For the most part there is no difference between advising functions and
;; advising subrs. There is one situation though where one might have to write
;; slightly different advice code for subrs than for functions. This case
;; arises when one wants to access subr arguments in a before/around advice
;; when the arguments were determined by an interactive call to the subr.
;; Advice cannot determine what `interactive' form determines the interactive
;; behavior of the subr, hence, when it calls the original definition in an
;; interactive subr invocation it has to use `call-interactively' to generate
;; the proper interactive behavior. Thus up to that call the arguments of the
;; interactive subr will be nil. For example, the following advice for
;; `kill-buffer' will not work in an interactive invocation...
;;
;; (defadvice kill-buffer (before fg-kill-buffer-hook first act preact comp)
;;   (my-before-kill-buffer-hook (ad-get-arg 0)))
;; kill-buffer
;;
;; ...because the buffer argument will be nil in that case. The way out of
;; this dilemma is to provide an `interactive' specification that mirrors
;; the interactive behavior of the unadvised subr, for example, the following
;; will do the right thing even when `kill-buffer' is called interactively:
;;
;; (defadvice kill-buffer (before fg-kill-buffer-hook first act preact comp)
;;   (interactive "bKill buffer: ")
;;   (my-before-kill-buffer-hook (ad-get-arg 0)))
;; kill-buffer
;;
;; @@ Advising macros:
;; ===================
;; Advising macros is slightly different because there are two significant
;; time points in the invocation of a macro: Expansion and evaluation time.
;; For an advised macro instead of evaluating the original definition we
;; use `macroexpand', that is, changing argument values and binding
;; environments by pieces of advice has an affect during macro expansion
;; but not necessarily during evaluation. In particular, any side effects
;; of pieces of advice will occur during macro expansion.  To also affect
;; the behavior during evaluation time one has to change the value of
;; `ad-return-value' in a piece of after advice. For example:
;;
;; (defmacro foom (x)
;;   (` (list (, x))))
;; foom
;;
;; (foom '(a))
;; ((a))
;;
;; (defadvice foom (before fg-print-x act)
;;   "Print the value of X."
;;   (print x))
;; foom
;;
;; The following works as expected because evaluation immediately follows
;; macro expansion:
;;
;; (foom '(a))
;; (quote (a))
;; ((a))
;;
;; However, the printing happens during expansion (or byte-compile) time:
;;
;; (macroexpand '(foom '(a)))
;; (quote (a))
;; (list (quote (a)))
;;
;; If we want it to happen during evaluation time we have to do the 
;; following (first remove the old advice):
;;
;; (ad-remove-advice 'foom 'before 'fg-print-x)
;; nil
;;
;; (defadvice foom (after fg-print-x act)
;;   "Print the value of X."
;;   (setq ad-return-value
;;         (` (progn (print (, x))
;;                   (, ad-return-value)))))
;; foom
;;
;; (macroexpand '(foom '(a)))
;; (progn (print (quote (a))) (list (quote (a))))
;;
;; (foom '(a))
;; (a)
;; ((a))
;;
;; While this method might seem somewhat cumbersome, it is very general
;; because it allows one to influence macro expansion as well as evaluation.
;; In general, advising macros should be a rather rare activity anyway, in
;; particular, because compile-time macro expansion takes away a lot of the
;; flexibility and effectiveness of the advice mechanism. Macros that were
;; compile-time expanded before the advice was activated will of course never
;; exhibit the advised behavior.
;;
;; @@ Advising special forms:
;; ==========================
;; Now for something that should be even more rare than advising macros:
;; Advising special forms. Because special forms are irregular in their
;; argument evaluation behavior (e.g., `setq' evaluates the second but not
;; the first argument) they have to be advised into macros. A dangerous
;; consequence of this is that the byte-compiler will not recognize them
;; as special forms anymore (well, in most cases) and use their expansion
;; rather than the proper byte-code. Also, because the original definition
;; of a special form cannot be `funcall'ed, `eval' has to be used instead
;; which is less efficient.
;;
;; MORAL: Do not advise special forms unless you are completely sure about
;;        what you are doing (some of the forward advice behavior is
;;        implemented via advice of the special forms `defun' and `defmacro').
;;        As a safety measure one should always do `ad-deactivate-all' before
;;        one byte-compiles a file to avoid any interference of advised
;;        special forms.
;;
;; Apart from the safety concerns advising special forms is not any different
;; from advising plain functions or subrs.


;;; Code:

;; @ Advice implementation:
;; ========================

;; @@ Compilation idiosyncrasies:
;; ==============================

;; `defadvice' expansion needs quite a few advice functions and variables,
;; hence, I need to preload the file before it can be compiled.  To avoid
;; interference of bogus compiled files I always preload the source file:
(provide 'advice-preload)
;; During a normal load this is a noop:
(require 'advice-preload "advice.el")


;; @@ Variable definitions:
;; ========================

(defconst ad-version "2.11")

(defmacro ad-lemacs-p ()
  ;;Expands into Non-nil constant if we run Lucid's version of Emacs-19.
  ;;Unselected conditional code will be optimized away during compilation.
  (string-match "Lucid" emacs-version))

;;;###autoload
(defvar ad-start-advice-on-load t
  "*Non-nil will start Advice magic when this file gets loaded.
Also see function `ad-start-advice'.")

;;;###autoload
(defvar ad-activate-on-definition nil
  "*Non-nil means automatic advice activation at function definition.
Set this variable to t if you want to enable forward advice (which is
automatic advice activation of a previously undefined function at the
point the function gets defined/loaded/autoloaded).  The value of this
variable takes effect only during the execution of `ad-start-advice'. 
If non-nil it will enable definition hooks regardless of the value
of `ad-enable-definition-hooks'.")

;;;###autoload
(defvar ad-redefinition-action 'warn
  "*Defines what to do with redefinitions during de/activation.
Redefinition occurs if a previously activated function that already has an
original definition associated with it gets redefined and then de/activated.
In such a case we can either accept the current definition as the new
original definition, discard the current definition and replace it with the
old original, or keep it and raise an error.  The values `accept', `discard',
`error' or `warn' govern what will be done.  `warn' is just like `accept' but
it additionally prints a warning message.  All other values will be
interpreted as `error'.")

;;;###autoload
(defvar ad-definition-hooks nil
  "*List of hooks to be run after a function definition.
The variable `ad-defined-function' will be bound to the name of
the currently defined function when the hook function is run.")

;;;###autoload
(defvar ad-enable-definition-hooks nil
  "*Non-nil will enable hooks to be run on function definition.
Setting this variable is a noop unless the value of
`ad-activate-on-definition' (which see) is nil.")


;; @@ Some utilities:
;; ==================

;; We don't want the local arguments to interfere with anything
;; referenced in the supplied functions => the cryptic casing:
(defun ad-substitute-tree (sUbTrEe-TeSt fUnCtIoN tReE)
  ;;"Substitutes qualifying subTREEs with result of FUNCTION(subTREE).
  ;;Only proper subtrees are considered, for example, if TREE is (1 (2 (3)) 4)
  ;;then the subtrees will be 1 (2 (3)) 2 (3) 3 4, dotted structures are
  ;;allowed too.  Once a qualifying subtree has been found its subtrees will
  ;;not be considered anymore.  (ad-substitute-tree 'atom 'identity tree)
  ;;generates a copy of TREE."
  (cond ((consp tReE)
         (cons (if (funcall sUbTrEe-TeSt (car tReE))
                   (funcall fUnCtIoN (car tReE))
                 (if (consp (car tReE))
                     (ad-substitute-tree sUbTrEe-TeSt fUnCtIoN (car tReE))
                   (car tReE)))
               (ad-substitute-tree sUbTrEe-TeSt fUnCtIoN (cdr tReE))))
        ((funcall sUbTrEe-TeSt tReE)
         (funcall fUnCtIoN tReE))
        (t tReE)))

;; this is just faster than `ad-substitute-tree':
(defun ad-copy-tree (tree)
  ;;"Returns a copy of the list structure of TREE."
  (cond ((consp tree)
	 (cons (ad-copy-tree (car tree))
	       (ad-copy-tree (cdr tree))))
	(t tree)))

(defmacro ad-dolist (varform &rest body)
  "A Common-Lisp-style dolist iterator with the following syntax:

    (ad-dolist (VAR INIT-FORM [RESULT-FORM])
       BODY-FORM...)

which will iterate over the list yielded by INIT-FORM binding VAR to the
current head at every iteration.  If RESULT-FORM is supplied its value will
be returned at the end of the iteration, nil otherwise.  The iteration can be
exited prematurely with `(ad-do-return [VALUE])'."
  (let ((expansion
         (` (let ((ad-dO-vAr (, (car (cdr varform))))
		  (, (car varform)))
	      (while ad-dO-vAr
		(setq (, (car varform)) (car ad-dO-vAr))
		(,@ body)
		;;work around a backquote bug:
		;;(` ((,@ '(foo)) (bar))) => (append '(foo) '(((bar)))) wrong
		;;(` ((,@ '(foo)) (, '(bar)))) => (append '(foo) (list '(bar)))
		(, '(setq ad-dO-vAr (cdr ad-dO-vAr))))
	      (, (car (cdr (cdr varform))))))))
    ;;ok, this wastes some cons cells but only during compilation:
    (if (catch 'contains-return
	  (ad-substitute-tree
	   (function (lambda (subtree)
		       (cond ((eq (car-safe subtree) 'ad-dolist))
			     ((eq (car-safe subtree) 'ad-do-return)
			      (throw 'contains-return t)))))
	   'identity body)
	  nil)
	(` (catch 'ad-dO-eXiT (, expansion)))
      expansion)))

(defmacro ad-do-return (value)
  (` (throw 'ad-dO-eXiT (, value))))

(if (not (get 'ad-dolist 'lisp-indent-hook))
    (put 'ad-dolist 'lisp-indent-hook 1))


;; @@ Save real definitions of subrs used by Advice:
;; =================================================
;; Advice depends on the real, unmodified functionality of various subrs, 
;; we save them here so advised versions will not interfere (eventually,
;; we will save all subrs used in code generated by Advice):

(defmacro ad-save-real-definition (function)
  (let ((saved-function (intern (format "ad-real-%s" function))))
    ;; Make sure the compiler is loaded during macro expansion:
    (require 'byte-compile "bytecomp")
    (` (if (not (fboundp '(, saved-function)))
	   (progn (fset '(, saved-function) (symbol-function '(, function)))
		  ;; Copy byte-compiler properties:
		  (,@ (if (get function 'byte-compile)
			  (` ((put '(, saved-function) 'byte-compile
				   '(, (get function 'byte-compile)))))))
		  (,@ (if (get function 'byte-opcode)
			  (` ((put '(, saved-function) 'byte-opcode
				   '(, (get function 'byte-opcode))))))))))))

(defun ad-save-real-definitions ()
  ;; Macro expansion will hardcode the values of the various byte-compiler
  ;; properties into the compiled version of this function such that the
  ;; proper values will be available at runtime without loading the compiler:
  (ad-save-real-definition fset)
  (ad-save-real-definition documentation)
  (ad-save-real-definition byte-code)
  (put 'ad-real-byte-code 'byte-compile nil))

(ad-save-real-definitions)


;; @@ Advice info access fns:
;; ==========================

;; Advice information for a particular function is stored on the
;; advice-info property of the function symbol.  It is stored as an
;; alist of the following format:
;;
;;      ((active . t/nil)
;;       (before adv1 adv2 ...)
;;       (around adv1 adv2 ...)
;;       (after  adv1 adv2 ...)
;;       (activation  adv1 adv2 ...)
;;       (deactivation  adv1 adv2 ...)
;;       (origname . <symbol fbound to origdef>)
;;       (cache . (<advised-definition> . <id>)))

;; List of currently advised though not necessarily activated functions
;; (this list is maintained as a completion table):
(defvar ad-advised-functions nil)

(defmacro ad-pushnew-advised-function (function)
  ;;"Add FUNCTION to `ad-advised-functions' unless its already there."
  (` (if (not (assoc (symbol-name (, function)) ad-advised-functions))
	 (setq ad-advised-functions
	       (cons (list (symbol-name (, function)))
		     ad-advised-functions)))))

(defmacro ad-pop-advised-function (function)
  ;;"Remove FUNCTION from `ad-advised-functions'."
  (` (setq ad-advised-functions
	   (delq (assoc (symbol-name (, function)) ad-advised-functions)
		 ad-advised-functions))))

(defmacro ad-do-advised-functions (varform &rest body)
  ;;"`ad-dolist'-style iterator that maps over `ad-advised-functions'.
  ;;     (ad-do-advised-functions (VAR [RESULT-FORM])
  ;;         BODY-FORM...)
  ;;Also see `ad-dolist'.  On each iteration VAR will be bound to the
  ;;name of an advised function (a symbol)."
  (` (ad-dolist ((, (car varform))
		 ad-advised-functions
		 (, (car (cdr varform))))
       (setq (, (car varform)) (intern (car (, (car varform)))))
       (,@ body))))

(if (not (get 'ad-do-advised-functions 'lisp-indent-hook))
    (put 'ad-do-advised-functions 'lisp-indent-hook 1))

(defmacro ad-get-advice-info (function)
  (` (get (, function) 'ad-advice-info)))

(defmacro ad-set-advice-info (function advice-info)
  (` (put (, function) 'ad-advice-info (, advice-info))))

(defmacro ad-copy-advice-info (function)
  (` (ad-copy-tree (get (, function) 'ad-advice-info))))

(defmacro ad-is-advised (function)
  ;;"Returns non-nil if FUNCTION has any advice info associated with it.
  ;;This does not mean that the advice is also active."
  (list 'ad-get-advice-info function))

(defun ad-initialize-advice-info (function)
  ;;"Initializes the advice info for FUNCTION.
  ;;Assumes that FUNCTION has not yet been advised."
  (ad-pushnew-advised-function function)
  (ad-set-advice-info function (list (cons 'active nil))))

(defmacro ad-get-advice-info-field (function field)
  ;;"Retrieves the value of the advice info FIELD of FUNCTION."
  (` (cdr (assq (, field) (ad-get-advice-info (, function))))))

(defun ad-set-advice-info-field (function field value)
  ;;"Destructively modifies VALUE of the advice info FIELD of FUNCTION."
  (and (ad-is-advised function)
       (cond ((assq field (ad-get-advice-info function))
	      ;; A field with that name is already present:
              (rplacd (assq field (ad-get-advice-info function)) value))
	     (t;; otherwise, create a new field with that name:
	      (nconc (ad-get-advice-info function)
		     (list (cons field value)))))))

;; Don't make this a macro so we can use it as a predicate:
(defun ad-is-active (function)
  ;;"non-nil if FUNCTION is advised and activated."
  (ad-get-advice-info-field function 'active))


;; @@ Access fns for single pieces of advice and related predicates:
;; =================================================================

(defun ad-make-advice (name protect enable definition)
  "Constructs single piece of advice to be stored in some advice-info.
NAME should be a non-nil symbol, PROTECT and ENABLE should each be
either t or nil, and DEFINITION should be a list of the form
`(advice lambda ARGLIST [DOCSTRING] [INTERACTIVE-FORM] BODY...)'."
  (list name protect enable definition))

;; ad-find-advice uses the alist structure directly ->
;; change if this data structure changes!!
(defmacro ad-advice-name (advice)
  (list 'car advice))
(defmacro ad-advice-protected (advice)
  (list 'nth 1 advice))
(defmacro ad-advice-enabled (advice)
  (list 'nth 2 advice))
(defmacro ad-advice-definition (advice)
  (list 'nth 3 advice))

(defun ad-advice-set-enabled (advice flag)
  (rplaca (cdr (cdr advice)) flag))

(defun ad-class-p (thing)
  (memq thing ad-advice-classes))
(defun ad-name-p (thing)
  (and thing (symbolp thing)))
(defun ad-position-p (thing)
  (or (natnump thing)
      (memq thing '(first last))))


;; @@ Advice access functions:
;; ===========================

;; List of defined advice classes:
(defvar ad-advice-classes '(before around after activation deactivation))

(defun ad-has-enabled-advice (function class)
  ;;"True if at least one of FUNCTION's advices in CLASS is enabled."
  (ad-dolist (advice (ad-get-advice-info-field function class))
    (if (ad-advice-enabled advice) (ad-do-return t))))

(defun ad-has-redefining-advice (function)
  ;;"True if FUNCTION's advice info defines at least 1 redefining advice.
  ;;Redefining advices affect the construction of an advised definition."
  (and (ad-is-advised function)
       (or (ad-has-enabled-advice function 'before)
	   (ad-has-enabled-advice function 'around)
	   (ad-has-enabled-advice function 'after))))

(defun ad-has-any-advice (function)
  ;;"True if the advice info of FUNCTION defines at least one advice."
  (and (ad-is-advised function)
       (ad-dolist (class ad-advice-classes nil)
	 (if (ad-get-advice-info-field function class)
	     (ad-do-return t)))))

(defun ad-get-enabled-advices (function class)
  ;;"Returns the list of enabled advices of FUNCTION in CLASS."
  (let (enabled-advices)
    (ad-dolist (advice (ad-get-advice-info-field function class))
      (if (ad-advice-enabled advice)
	  (setq enabled-advices (cons advice enabled-advices))))
    (reverse enabled-advices)))


;; @@ Access functions for original definitions:
;; ============================================
;; The advice-info of an advised function contains its `origname' which is
;; a symbol that is fbound to the original definition available at the first
;; proper activation of the function after a legal re/definition.  If the
;; original was defined via fcell indirection then `origname' will be defined
;; just so.  Hence, to get hold of the actual original definition of a function
;; we need to use `ad-real-orig-definition'.

(defun ad-make-origname (function)
  ;;"Makes name to be used to call the original FUNCTION."
  (intern (format "ad-Orig-%s" function)))

(defmacro ad-get-orig-definition (function)
  (` (let ((origname (ad-get-advice-info-field (, function) 'origname)))
       (if (fboundp origname)
	   (symbol-function origname)))))

(defmacro ad-set-orig-definition (function definition)
  (` (ad-real-fset
      (ad-get-advice-info-field function 'origname) (, definition))))

(defmacro ad-clear-orig-definition (function)
  (` (fmakunbound (ad-get-advice-info-field (, function) 'origname))))


;; @@ Interactive input functions:
;; ===============================

(defun ad-read-advised-function (&optional prompt predicate default)
  ;;"Reads name of advised function with completion from the minibuffer.
  ;;An optional PROMPT will be used to prompt for the function.  PREDICATE
  ;;plays the same role as for `try-completion' (which see).  DEFAULT will
  ;;be returned on empty input (defaults to the first advised function for
  ;;which PREDICATE returns non-nil)."
  (if (null ad-advised-functions)
      (error "ad-read-advised-function: There are no advised functions"))
  (setq default
	(or default
	    (ad-do-advised-functions (function)
	      (if (or (null predicate)
		      (funcall predicate function))
		  (ad-do-return function)))
	    (error "ad-read-advised-function: %s"
		   "There are no qualifying advised functions")))
  (let* ((ad-pReDiCaTe predicate)
	 (function
	  (completing-read
	   (format "%s(default %s) " (or prompt "Function: ") default)
	   ad-advised-functions
	   (if predicate
	       (function
		(lambda (function)
		  ;; Oops, no closures - the joys of dynamic scoping:
		  ;; `predicate' clashed with the `predicate' argument
		  ;; of Lemacs' `completing-read'.....
		  (funcall ad-pReDiCaTe (intern (car function))))))
	   t)))
    (if (equal function "")
	(if (ad-is-advised default)
	    default
	  (error "ad-read-advised-function: `%s' is not advised" default))
      (intern function))))

(defvar ad-advice-class-completion-table
  (mapcar '(lambda (class) (list (symbol-name class)))
	  ad-advice-classes))

(defun ad-read-advice-class (function &optional prompt default)
  ;;"Reads a legal advice class with completion from the minibuffer.
  ;;An optional PROMPT will be used to prompt for the class.  DEFAULT will
  ;;be returned on empty input (defaults to the first non-empty advice
  ;;class of FUNCTION)."
  (setq default
	(or default
	    (ad-dolist (class ad-advice-classes)
	      (if (ad-get-advice-info-field function class)
		  (ad-do-return class)))
	    (error "ad-read-advice-class: `%s' has no advices" function)))
  (let ((class (completing-read
		(format "%s(default %s) " (or prompt "Class: ") default)
		ad-advice-class-completion-table nil t)))
    (if (equal class "")
	default
      (intern class))))

(defun ad-read-advice-name (function class &optional prompt)
  ;;"Reads name of existing advice of CLASS for FUNCTION with completion.
  ;;An optional PROMPT is used to prompt for the name."
  (let* ((name-completion-table
          (mapcar (function (lambda (advice)
			      (list (symbol-name (ad-advice-name advice)))))
		  (ad-get-advice-info-field function class)))
	 (default
	   (if (null name-completion-table)
	       (error "ad-read-advice-name: `%s' has no %s advice"
		      function class)
	     (car (car name-completion-table))))
	 (prompt (format "%s(default %s) " (or prompt "Name: ") default))
	 (name (completing-read prompt name-completion-table nil t)))
    (if (equal name "")
	(intern default)
      (intern name))))

(defun ad-read-advice-specification (&optional prompt)
  ;;"Reads a complete function/class/name specification from minibuffer.
  ;;The list of read symbols will be returned.  The optional PROMPT will
  ;;be used to prompt for the function."
  (let* ((function (ad-read-advised-function prompt))
	 (class (ad-read-advice-class function))
	 (name (ad-read-advice-name function class)))
    (list function class name)))

;; Use previous regexp as a default:
(defvar ad-last-regexp "")

(defun ad-read-regexp (&optional prompt)
  ;;"Reads a regular expression from the minibuffer."
  (let ((regexp (read-from-minibuffer
		 (concat (or prompt "Regular expression: ")
			 (if (equal ad-last-regexp "") ""
			   (format "(default \"%s\") " ad-last-regexp))))))
    (setq ad-last-regexp
	  (if (equal regexp "") ad-last-regexp regexp))))


;; @@ Finding, enabling, adding and removing pieces of advice:
;; ===========================================================

(defmacro ad-find-advice (function class name)
  ;;"Finds the first advice of FUNCTION in CLASS with NAME."
  (` (assq (, name) (ad-get-advice-info-field (, function) (, class)))))

(defun ad-advice-position (function class name)
  ;;"Returns position of first advice of FUNCTION in CLASS with NAME."
  (let* ((found-advice (ad-find-advice function class name))
	 (advices (ad-get-advice-info-field function class)))
    (if found-advice
	(- (length advices) (length (memq found-advice advices))))))

(defun ad-find-some-advice (function class name)
  "Finds the first of FUNCTION's advices in CLASS matching NAME.
NAME can be a symbol or a regular expression matching part of an advice name.
If CLASS is `any' all legal advice classes will be checked."
  (if (ad-is-advised function)
      (let (found-advice)
	(ad-dolist (advice-class ad-advice-classes)
	  (if (or (eq class 'any) (eq advice-class class))
	      (setq found-advice
		    (ad-dolist (advice (ad-get-advice-info-field
					function advice-class))
		      (if (or (and (stringp name)
				   (string-match
				    name (symbol-name
					  (ad-advice-name advice))))
			      (eq name (ad-advice-name advice)))
			  (ad-do-return advice)))))
	  (if found-advice (ad-do-return found-advice))))))

(defun ad-enable-advice-internal (function class name flag)
  ;;"Sets enable FLAG of FUNCTION's advices in CLASS matching NAME.
  ;;If NAME is a string rather than a symbol then it's interpreted as a regular
  ;;expression and all advices whose name contain a match for it will be 
  ;;affected.  If CLASS is `any' advices in all legal advice classes will be 
  ;;considered.  The number of changed advices will be returned (or nil if 
  ;;FUNCTION was not advised)."
  (if (ad-is-advised function)
      (let ((matched-advices 0))
	(ad-dolist (advice-class ad-advice-classes)
	  (if (or (eq class 'any) (eq advice-class class))
	      (ad-dolist (advice (ad-get-advice-info-field
				  function advice-class))
		(cond ((or (and (stringp name)
				(string-match
				 name (symbol-name (ad-advice-name advice))))
			   (eq name (ad-advice-name advice)))
		       (setq matched-advices (1+ matched-advices))
		       (ad-advice-set-enabled advice flag))))))
	matched-advices)))

(defun ad-enable-advice (function class name)
  "Enables the advice of FUNCTION with CLASS and NAME."
  (interactive (ad-read-advice-specification "Enable advice of: "))
  (if (ad-is-advised function)
      (if (eq (ad-enable-advice-internal function class name t) 0)
	  (error "ad-enable-advice: `%s' has no %s advice matching `%s'"
		 function class name))
    (error "ad-enable-advice: `%s' is not advised" function)))

(defun ad-disable-advice (function class name)
  "Disables the advice of FUNCTION with CLASS and NAME."
  (interactive (ad-read-advice-specification "Disable advice of: "))
  (if (ad-is-advised function)
      (if (eq (ad-enable-advice-internal function class name nil) 0)
	  (error "ad-disable-advice: `%s' has no %s advice matching `%s'"
		 function class name))
    (error "ad-disable-advice: `%s' is not advised" function)))

(defun ad-enable-regexp-internal (regexp class flag)
  ;;"Sets enable FLAGs of all CLASS advices whose name contains a REGEXP match.
  ;;If CLASS is `any' all legal advice classes are considered.  The number of
  ;;affected advices will be returned."
  (let ((matched-advices 0))
    (ad-do-advised-functions (advised-function)
      (setq matched-advices
	    (+ matched-advices
	       (or (ad-enable-advice-internal
		    advised-function class regexp flag)
		   0))))
    matched-advices))

(defun ad-enable-regexp (regexp)
  "Enables all advices with names that contain a match for REGEXP.
All currently advised functions will be considered."
  (interactive
   (list (ad-read-regexp "Enable advices via regexp: ")))
  (let ((matched-advices (ad-enable-regexp-internal regexp 'any t)))
    (if (interactive-p)
	(message "%d matching advices enabled" matched-advices))
    matched-advices))

(defun ad-disable-regexp (regexp)
  "Disables all advices with names that contain a match for REGEXP.
All currently advised functions will be considered."
  (interactive
   (list (ad-read-regexp "Disable advices via regexp: ")))
  (let ((matched-advices (ad-enable-regexp-internal regexp 'any nil)))
    (if (interactive-p)
	(message "%d matching advices disabled" matched-advices))
    matched-advices))

(defun ad-remove-advice (function class name)
  "Removes FUNCTION's advice with NAME from its advices in CLASS.
If such an advice was found it will be removed from the list of advices
in that CLASS."
  (interactive (ad-read-advice-specification "Remove advice of: "))
  (if (ad-is-advised function)
      (let* ((advice-to-remove (ad-find-advice function class name)))
	(if advice-to-remove
	    (ad-set-advice-info-field
	     function class
	     (delq advice-to-remove (ad-get-advice-info-field function class)))
	  (error "ad-remove-advice: `%s' has no %s advice `%s'"
		 function class name)))
    (error "ad-remove-advice: `%s' is not advised" function)))

;;;###autoload
(defun ad-add-advice (function advice class position)
  "Adds a piece of ADVICE to FUNCTION's list of advices in CLASS.
If FUNCTION already has one or more pieces of advice of the specified
CLASS then POSITION determines where the new piece will go.  The value
of POSITION can either be `first', `last' or a number where 0 corresponds
to `first'.  Numbers outside the range will be mapped to the closest
extreme position.  If there was already a piece of ADVICE with the same
name, then the position argument will be ignored and the old advice
will be overwritten with the new one.
    If the FUNCTION was not advised already, then its advice info will be 
initialized.  Redefining a piece of advice whose name is part of the cache-id
will clear the cache."
  (cond ((not (ad-is-advised function))
         (ad-initialize-advice-info function)
	 (ad-set-advice-info-field
	  function 'origname (ad-make-origname function))))
  (let* ((previous-position
	  (ad-advice-position function class (ad-advice-name advice)))
	 (advices (ad-get-advice-info-field function class))
	 ;; Determine a numerical position for the new advice:
	 (position (cond (previous-position)
			 ((eq position 'first) 0)
			 ((eq position 'last) (length advices))
			 ((numberp position)
			  (max 0 (min position (length advices))))
			 (t 0))))
    ;; Check whether we have to clear the cache:
    (if (memq (ad-advice-name advice) (ad-get-cache-class-id function class))
        (ad-clear-cache function))
    (if previous-position
	(setcar (nthcdr position advices) advice)
      (if (= position 0)
	  (ad-set-advice-info-field function class (cons advice advices))
	(setcdr (nthcdr (1- position) advices)
		(cons advice (nthcdr position advices)))))))


;; @@ Accessing and manipulating function definitions:
;; ===================================================

(defmacro ad-macrofy (definition)
  ;;"Takes a lambda function DEFINITION and makes a macro out of it."
  (` (cons 'macro (, definition))))

(defmacro ad-lambdafy (definition)
  ;;"Takes a macro function DEFINITION and makes a lambda out of it."
  (` (cdr (, definition))))

;; There is no way to determine whether some subr is a special form or not,
;; hence we need this list (which is probably out of date):
(defvar ad-special-forms
  (mapcar 'symbol-function
	  '(and catch cond condition-case defconst defmacro
			       defun defvar function if interactive let let*
			       or prog1 prog2 progn quote save-excursion
                               save-restriction save-window-excursion setq
			       setq-default unwind-protect while
			       with-output-to-temp-buffer)))

(defmacro ad-special-form-p (definition)
  ;;"non-nil if DEFINITION is a special form."
  (list 'memq definition 'ad-special-forms))

(defmacro ad-interactive-p (definition)
  ;;"non-nil if DEFINITION can be called interactively."
  (list 'commandp definition))

(defmacro ad-subr-p (definition)
  ;;"non-nil if DEFINITION is a subr."
  (list 'subrp definition))

(defmacro ad-macro-p (definition)
  ;;"non-nil if DEFINITION is a macro."
  (` (eq (car-safe (, definition)) 'macro)))

(defmacro ad-lambda-p (definition)
  ;;"non-nil if DEFINITION is a lambda expression."
  (` (eq (car-safe (, definition)) 'lambda)))

;; see ad-make-advice for the format of advice definitions:
(defmacro ad-advice-p (definition)
  ;;"non-nil if DEFINITION is a piece of advice."
  (` (eq (car-safe (, definition)) 'advice)))

;; Emacs/Lemacs cross-compatibility
;; (compiled-function-p is an obsolete function in Emacs):
(if (and (not (fboundp 'byte-code-function-p))
	 (fboundp 'compiled-function-p))
    (ad-real-fset 'byte-code-function-p 'compiled-function-p))

(defmacro ad-compiled-p (definition)
  ;;"non-nil if DEFINITION is a compiled byte-code object."
  (` (or (byte-code-function-p (, definition))
	 (and (ad-macro-p (, definition))
	      (byte-code-function-p (ad-lambdafy (, definition)))))))

(defmacro ad-compiled-code (compiled-definition)
  ;;"Returns the byte-code object of a COMPILED-DEFINITION."
  (` (if (ad-macro-p (, compiled-definition))
	 (ad-lambdafy (, compiled-definition))
       (, compiled-definition))))

(defun ad-lambda-expression (definition)
  ;;"Returns the lambda expression of a function/macro/advice DEFINITION."
  (cond ((ad-lambda-p definition)
	 definition)
	((ad-macro-p definition)
	 (ad-lambdafy definition))
	((ad-advice-p definition)
	 (cdr definition))
	(t nil)))

(defun ad-arglist (definition &optional name)
  ;;"Returns the argument list of DEFINITION.
  ;;If DEFINITION could be from a subr then its NAME should be
  ;;supplied to make subr arglist lookup more efficient."
  (cond ((ad-compiled-p definition)
	 (aref (ad-compiled-code definition) 0))
	((consp definition)
	 (car (cdr (ad-lambda-expression definition))))
	((ad-subr-p definition)
	 (if name
	     (ad-subr-arglist name)
	   ;; otherwise get it from its printed representation:
	   (setq name (format "%s" definition))
	   (string-match "^#<subr \\([^>]+\\)>$" name)
	   (ad-subr-arglist
	    (intern (substring name (match-beginning 1) (match-end 1))))))))

;; Store subr-args as `((arg1 arg2 ...))' so I can distinguish
;; a defined empty arglist `(nil)' from an undefined arglist:
(defmacro ad-define-subr-args (subr arglist)
  (` (put (, subr) 'ad-subr-arglist (list (, arglist)))))
(defmacro ad-undefine-subr-args (subr)
  (` (put (, subr) 'ad-subr-arglist nil)))
(defmacro ad-subr-args-defined-p (subr)
  (` (get (, subr) 'ad-subr-arglist)))
(defmacro ad-get-subr-args (subr)
  (` (car (get (, subr) 'ad-subr-arglist))))

(defun ad-subr-arglist (subr-name)
  ;;"Retrieve arglist of the subr with SUBR-NAME.
  ;;Either use the one stored under the `ad-subr-arglist' property,
  ;;or try to retrieve it from the docstring and cache it under
  ;;that property, or otherwise use `(&rest ad-subr-args)'."
  (cond ((ad-subr-args-defined-p subr-name)
	 (ad-get-subr-args subr-name))
	;; says jwz: Should use this for Lemacs 19.8 and above:
	;;((fboundp 'subr-min-args)
	;;  ...)
	;; says hans: I guess what Jamie means is that I should use the values
	;; of `subr-min-args' and `subr-max-args' to construct the subr arglist
	;; without having to look it up via parsing the docstring, e.g.,
	;; values 1 and 2 would suggest `(arg1 &optional arg2)' as an
	;; argument list.  However, that won't work because there is no
	;; way to distinguish a subr with args `(a &optional b &rest c)' from
	;; one with args `(a &rest c)' using that mechanism. Also, the argument
	;; names from the docstring are more meaningful. Hence, I'll stick with
	;; the old way of doing things.
	(t (let ((doc (ad-real-documentation subr-name t)))
	     (cond ((and doc
			 (string-match
			  "[\n\t ]*\narguments: ?\\((.*)\\)\n?\\'" doc))
		    (ad-define-subr-args
		     subr-name
		     (car (read-from-string
			   doc (match-beginning 1) (match-end 1))))
		    (ad-get-subr-args subr-name))
		   (t '(&rest ad-subr-args)))))))

(defun ad-docstring (definition)
  ;;"Returns the unexpanded docstring of DEFINITION."
  (let ((docstring
	 (if (ad-compiled-p definition)
	     (ad-real-documentation definition t)
	   (car (cdr (cdr (ad-lambda-expression definition)))))))
    (if (or (stringp docstring)
	    (natnump docstring))
	docstring)))

(defun ad-interactive-form (definition)
  ;;"Returns the interactive form of DEFINITION."
  (cond ((ad-compiled-p definition)
	 (and (commandp definition)
	      (list 'interactive (aref (ad-compiled-code definition) 5))))
	((or (ad-advice-p definition)
	     (ad-lambda-p definition))
	 (commandp (ad-lambda-expression definition)))))

(defun ad-body-forms (definition)
  ;;"Returns the list of body forms of DEFINITION."
  (cond ((ad-compiled-p definition)
	 nil)
	((consp definition)
	 (nthcdr (+ (if (ad-docstring definition) 1 0)
		    (if (ad-interactive-form definition) 1 0))
		 (cdr (cdr (ad-lambda-expression definition)))))))

;; Matches the docstring of an advised definition.
;; The first group of the regexp matches the function name:
(defvar ad-advised-definition-docstring-regexp "^\\$ad-doc: \\(.+\\)\\$$")

(defun ad-make-advised-definition-docstring (function)
  ;; Makes an identifying docstring for the advised definition of FUNCTION.
  ;; Put function name into the documentation string so we can infer
  ;; the name of the advised function from the docstring.  This is needed
  ;; to generate a proper advised docstring even if we are just given a
  ;; definition (also see the defadvice for `documentation'):
  (format "$ad-doc: %s$" (prin1-to-string function)))

(defun ad-advised-definition-p (definition)
  ;;"non-nil if DEFINITION was generated from advice information."
  (if (or (ad-lambda-p definition)
	  (ad-macro-p definition)
	  (ad-compiled-p definition))
      (let ((docstring (ad-docstring definition)))
	(and (stringp docstring)
	     (string-match
	      ad-advised-definition-docstring-regexp docstring)))))

(defun ad-definition-type (definition)
  ;;"Returns symbol that describes the type of DEFINITION."
  (if (ad-macro-p definition)
      'macro
    (if (ad-subr-p definition)
	(if (ad-special-form-p definition)
	    'special-form
	  'subr)
      (if (or (ad-lambda-p definition)
	      (ad-compiled-p definition))
	  'function
	(if (ad-advice-p definition)
	    'advice)))))

(defun ad-has-proper-definition (function)
  ;;"True if FUNCTION is a symbol with a proper definition.
  ;;For that it has to be fbound with a non-autoload definition."
  (and (symbolp function)
       (fboundp function)
       (not (eq (car-safe (symbol-function function)) 'autoload))))

;; The following two are necessary for the sake of packages such as
;; ange-ftp which redefine functions via fcell indirection:
(defun ad-real-definition (function)
  ;;"Finds FUNCTION's definition at the end of function cell indirection."
  (if (ad-has-proper-definition function)
      (let ((definition (symbol-function function)))
	(if (symbolp definition)
	    (ad-real-definition definition)
	  definition))))

(defun ad-real-orig-definition (function)
  ;;"Finds FUNCTION's real original definition starting from its `origname'."
  (if (ad-is-advised function)
      (ad-real-definition (ad-get-advice-info-field function 'origname))))

(defun ad-is-compilable (function)
  ;;"True if FUNCTION has an interpreted definition that can be compiled."
  (and (ad-has-proper-definition function)
       (or (ad-lambda-p (symbol-function function))
	   (ad-macro-p (symbol-function function)))
       (not (ad-compiled-p (symbol-function function)))))

(defun ad-compile-function (function)
  "Byte-compiles FUNCTION (or macro) if it is not yet compiled."
  (interactive "aByte-compile function: ")
  (if (ad-is-compilable function)
      (byte-compile function)))


;; @@ Constructing advised definitions:
;; ====================================
;;
;; Main design decisions about the form of advised definitions:
;;
;; A) How will original definitions be called?
;; B) What will argument lists of advised functions look like?
;;
;; Ad A)
;;    I chose to use function indirection for all four types of original
;;    definitions (functions, macros, subrs and special forms), i.e., create
;;    a unique symbol `ad-Orig-<name>' which is fbound to the original
;;    definition and call it according to type and arguments.  Functions and
;;    subrs that don't have any &rest arguments can be called directly in a
;;    `(ad-Orig-<name> ....)' form.  If they have a &rest argument we have to
;;    use `apply'.  Macros will be called with 
;;    `(macroexpand '(ad-Orig-<name> ....))', and special forms also need a
;;    form like that with `eval' instead of `macroexpand'.
;;
;; Ad B)
;;    Use original arguments where possible and `(&rest ad-subr-args)'
;;    otherwise, even though this seems to be more complicated and less
;;    uniform than a general `(&rest args)' approach.  My reason to still
;;    do it that way is that in most cases my approach leads to the more
;;    efficient form for the advised function, and portability (e.g., to
;;    make the same advice work regardless of whether something is a
;;    function or a subr) can still be achieved with argument access macros.


(defun ad-prognify (forms)
  (cond ((<= (length forms) 1)
	 (car forms))
	(t (cons 'progn forms))))

;; @@@ Accessing argument lists:
;; =============================

(defun ad-parse-arglist (arglist)
  ;;"Parses ARGLIST into its required, optional and rest parameters.
  ;;A three-element list is returned, where the 1st element is the list of
  ;;required arguments, the 2nd is the list of optional arguments, and the 3rd
  ;;is the name of an optional rest parameter (or nil)."
  (let* (required optional rest)
    (setq rest (car (cdr (memq '&rest arglist))))
    (if rest (setq arglist (reverse (cdr (memq '&rest (reverse arglist))))))
    (setq optional (cdr (memq '&optional arglist)))
    (if optional
	(setq required (reverse (cdr (memq '&optional (reverse arglist)))))
      (setq required arglist))
    (list required optional rest)))

(defun ad-retrieve-args-form (arglist)
  ;;"Generates a form which evaluates into names/values/types of ARGLIST.
  ;;When the form gets evaluated within a function with that argument list
  ;;it will result in a list with one entry for each argument, where the
  ;;first element of each entry is the name of the argument, the second
  ;;element is its actual current value, and the third element is either
  ;;`required', `optional' or `rest' depending on the type of the argument."
  (let* ((parsed-arglist (ad-parse-arglist arglist))
	 (rest (nth 2 parsed-arglist)))
    (` (list
	(,@ (mapcar (function
		     (lambda (req)
		       (` (list '(, req) (, req) 'required))))
		    (nth 0 parsed-arglist)))
	(,@ (mapcar (function
		     (lambda (opt)
		       (` (list '(, opt) (, opt) 'optional))))
		    (nth 1 parsed-arglist)))
	(,@ (if rest (list (` (list '(, rest) (, rest) 'rest)))))
	))))

(defun ad-arg-binding-field (binding field)
  (cond ((eq field 'name) (car binding))
	((eq field 'value) (car (cdr binding)))
	((eq field 'type) (car (cdr (cdr binding))))))

(defun ad-list-access (position list)
  (cond ((= position 0) list)
	((= position 1) (list 'cdr list))
	(t (list 'nthcdr position list))))

(defun ad-element-access (position list)
  (cond ((= position 0) (list 'car list))
	((= position 1) (` (car (cdr (, list)))))
	(t (list 'nth position list))))

(defun ad-access-argument (arglist index)
  ;;"Tells how to access ARGLIST's actual argument at position INDEX.
  ;;For a required/optional arg it simply returns it, if a rest argument has
  ;;to be accessed, it returns a list with the index and name."
  (let* ((parsed-arglist (ad-parse-arglist arglist))
	 (reqopt-args (append (nth 0 parsed-arglist)
			      (nth 1 parsed-arglist)))
	 (rest-arg (nth 2 parsed-arglist)))
    (cond ((< index (length reqopt-args))
	   (nth index reqopt-args))
	  (rest-arg
	   (list (- index (length reqopt-args)) rest-arg)))))

(defun ad-get-argument (arglist index)
  ;;"Returns form to access ARGLIST's actual argument at position INDEX."
  (let ((argument-access (ad-access-argument arglist index)))
    (cond ((consp argument-access)
	   (ad-element-access
	    (car argument-access) (car (cdr argument-access))))
	  (argument-access))))

(defun ad-set-argument (arglist index value-form)
  ;;"Returns form to set ARGLIST's actual arg at INDEX to VALUE-FORM."
  (let ((argument-access (ad-access-argument arglist index)))
    (cond ((consp argument-access)
	   ;; should this check whether there actually is something to set?
	   (` (setcar (, (ad-list-access
			  (car argument-access) (car (cdr argument-access))))
		      (, value-form))))
	  (argument-access
	   (` (setq (, argument-access) (, value-form))))
	  (t (error "ad-set-argument: No argument at position %d of `%s'"
		    index arglist)))))

(defun ad-get-arguments (arglist index)
  ;;"Returns form to access all actual arguments starting at position INDEX."
  (let* ((parsed-arglist (ad-parse-arglist arglist))
	 (reqopt-args (append (nth 0 parsed-arglist)
			      (nth 1 parsed-arglist)))
	 (rest-arg (nth 2 parsed-arglist))
	 args-form)
    (if (< index (length reqopt-args))
	(setq args-form (` (list (,@ (nthcdr index reqopt-args))))))
    (if rest-arg
	(if args-form
	    (setq args-form (` (nconc (, args-form) (, rest-arg))))
	  (setq args-form (ad-list-access (- index (length reqopt-args))
					  rest-arg))))
    args-form))

(defun ad-set-arguments (arglist index values-form)
  ;;"Makes form to assign elements of VALUES-FORM as actual ARGLIST args.
  ;;The assignment starts at position INDEX."
  (let ((values-index 0)
	argument-access set-forms)
    (while (setq argument-access (ad-access-argument arglist index))
      (if (symbolp argument-access)
	  (setq set-forms
		(cons (ad-set-argument
		       arglist index
		       (ad-element-access values-index 'ad-vAlUeS))
		      set-forms))
	(setq set-forms
	      (cons (if (= (car argument-access) 0)
			(list 'setq
			      (car (cdr argument-access))
			      (ad-list-access values-index 'ad-vAlUeS))
		      (list 'setcdr
			    (ad-list-access (1- (car argument-access))
					    (car (cdr argument-access)))
			    (ad-list-access values-index 'ad-vAlUeS)))
		    set-forms))
	;; terminate loop
	(setq arglist nil))
      (setq index (1+ index))
      (setq values-index (1+ values-index)))
    (if (null set-forms)
	(error "ad-set-arguments: No argument at position %d of `%s'"
	       index arglist)
      (if (= (length set-forms) 1)
	  ;; For exactly one set-form we can use values-form directly,...
	  (ad-substitute-tree
	   (function (lambda (form) (eq form 'ad-vAlUeS)))
	   (function (lambda (form) values-form))
	   (car set-forms))
	;; ...if we have more we have to bind it to a variable:
	(` (let ((ad-vAlUeS (, values-form)))
	     (,@ (reverse set-forms))
	     ;; work around the old backquote bug:
	     (, 'ad-vAlUeS)))))))

(defun ad-insert-argument-access-forms (definition arglist)
  ;;"Expands arg-access text macros in DEFINITION according to ARGLIST."
  (ad-substitute-tree
   (function
    (lambda (form)
      (or (eq form 'ad-arg-bindings)
	  (and (memq (car-safe form)
		     '(ad-get-arg ad-get-args ad-set-arg ad-set-args))
	       (integerp (car-safe (cdr form)))))))
   (function
    (lambda (form)
      (if (eq form 'ad-arg-bindings)
	  (ad-retrieve-args-form arglist)
	(let ((accessor (car form))
	      (index (car (cdr form)))
	      (val (car (cdr (ad-insert-argument-access-forms
			      (cdr form) arglist)))))
	  (cond ((eq accessor 'ad-get-arg)
		 (ad-get-argument arglist index))
		((eq accessor 'ad-set-arg)
		 (ad-set-argument arglist index val))
		((eq accessor 'ad-get-args)
		 (ad-get-arguments arglist index))
		((eq accessor 'ad-set-args)
		 (ad-set-arguments arglist index val)))))))
		   definition))

;; @@@ Mapping argument lists:
;; ===========================
;; Here is the problem:
;; Suppose function foo was called with (foo 1 2 3 4 5), and foo has the
;; argument list (x y &rest z), and we want to call the function bar which
;; has argument list (a &rest b) with a combination of x, y and z so that
;; the effect is just as if we had called (bar 1 2 3 4 5) directly. 
;; The mapping should work for any two argument lists.

(defun ad-map-arglists (source-arglist target-arglist)
  "Makes `funcall/apply' form to map SOURCE-ARGLIST to TARGET-ARGLIST.
The arguments supplied to TARGET-ARGLIST will be taken from SOURCE-ARGLIST just
as if they had been supplied to a function with TARGET-ARGLIST directly. 
Excess source arguments will be neglected, missing source arguments will be 
supplied as nil.  Returns a `funcall' or `apply' form with the second element
being `function' which has to be replaced by an actual function argument.
Example: `(ad-map-arglists '(a &rest args) '(w x y z))' will return
         `(funcall function a (car args) (car (cdr args)) (nth 2 args))'."
  (let* ((parsed-source-arglist (ad-parse-arglist source-arglist))
	 (source-reqopt-args (append (nth 0 parsed-source-arglist)
				     (nth 1 parsed-source-arglist)))
	 (source-rest-arg (nth 2 parsed-source-arglist))
	 (parsed-target-arglist (ad-parse-arglist target-arglist))
	 (target-reqopt-args (append (nth 0 parsed-target-arglist)
				     (nth 1 parsed-target-arglist)))
	 (target-rest-arg (nth 2 parsed-target-arglist))
	 (need-apply (and source-rest-arg target-rest-arg))
	 (target-arg-index -1))
    ;; This produces ``error-proof'' target function calls with the exception
    ;; of a case like (&rest a) mapped onto (x &rest y) where the actual args
    ;; supplied to A might not be enough to supply the required target arg X
    (append (list (if need-apply 'apply 'funcall) 'function)
	    (cond (need-apply
		   ;; `apply' can take care of that directly:
		   (append source-reqopt-args (list source-rest-arg)))
		  (t (mapcar (function
			      (lambda (arg)
				(setq target-arg-index (1+ target-arg-index))
				(ad-get-argument
				 source-arglist target-arg-index)))
			     (append target-reqopt-args
				     (and target-rest-arg
					  ;; If we have a rest arg gobble up
					  ;; remaining source args:
					  (nthcdr (length target-reqopt-args)
						  source-reqopt-args)))))))))

(defun ad-make-mapped-call (source-arglist target-arglist target-function)
  ;;"Makes form to call TARGET-FUNCTION with args from SOURCE-ARGLIST."
  (let* ((mapped-form (ad-map-arglists source-arglist target-arglist)))
    (if (eq (car mapped-form) 'funcall)
	(cons target-function (cdr (cdr mapped-form)))
      (prog1 mapped-form
	(setcar (cdr mapped-form) (list 'quote target-function))))))

;; @@@ Making an advised documentation string:
;; ===========================================
;; New policy: The documentation string for an advised function will be built
;; at the time the advised `documentation' function is called.  This has the
;; following advantages:
;;   1) command-key substitutions will automatically be correct
;;   2) No wasted string space due to big advised docstrings in caches or
;;      compiled files that contain preactivations
;; The overall overhead for this should be negligible because people normally
;; don't lookup documentation for the same function over and over again.

(defun ad-make-single-advice-docstring (advice class &optional style)
  (let ((advice-docstring (ad-docstring (ad-advice-definition advice))))
    (cond ((eq style 'plain)
	   advice-docstring)
	  ((eq style 'freeze)
	   (format "Permanent %s-advice `%s':%s%s"
		   class (ad-advice-name advice)
		   (if advice-docstring "\n" "")
		   (or advice-docstring "")))
	  (t (format "%s-advice `%s':%s%s"
		     (capitalize (symbol-name class)) (ad-advice-name advice)
		     (if advice-docstring "\n" "")
		     (or advice-docstring ""))))))

(defun ad-make-advised-docstring (function &optional style)
  ;;"Constructs a documentation string for the advised FUNCTION.
  ;;It concatenates the original documentation with the documentation
  ;;strings of the individual pieces of advice which will be formatted
  ;;according to STYLE.  STYLE can be `plain' or `freeze', everything else
  ;;will be interpreted as `default'.  The order of the advice documentation
  ;;strings corresponds to before/around/after and the individual ordering
  ;;in any of these classes."
  (let* ((origdef (ad-real-orig-definition function))
	 (origtype (symbol-name (ad-definition-type origdef)))
	 (origdoc
	  ;; Retrieve raw doc, key substitution will be taken care of later:
	  (ad-real-documentation origdef t))
	 paragraphs advice-docstring)
    (if origdoc (setq paragraphs (list origdoc)))
    (if (not (eq style 'plain))
	(setq paragraphs (cons (concat "This " origtype " is advised.")
			       paragraphs)))
    (ad-dolist (class ad-advice-classes)
      (ad-dolist (advice (ad-get-enabled-advices function class))
	(setq advice-docstring
	      (ad-make-single-advice-docstring advice class style))
	(if advice-docstring
	    (setq paragraphs (cons advice-docstring paragraphs)))))
    (if paragraphs
	;; separate paragraphs with blank lines:
	(mapconcat 'identity (nreverse paragraphs) "\n\n"))))

(defun ad-make-plain-docstring (function)
  (ad-make-advised-docstring function 'plain))
(defun ad-make-freeze-docstring (function)
  (ad-make-advised-docstring function 'freeze))

;; @@@ Accessing overriding arglists and interactive forms:
;; ========================================================

(defun ad-advised-arglist (function)
  ;;"Finds first defined arglist in FUNCTION's redefining advices."
  (ad-dolist (advice (append (ad-get-enabled-advices function 'before)
			     (ad-get-enabled-advices function 'around)
			     (ad-get-enabled-advices function 'after)))
    (let ((arglist (ad-arglist (ad-advice-definition advice))))
      (if arglist
	  ;; We found the first one, use it:
	  (ad-do-return arglist)))))

(defun ad-advised-interactive-form (function)
  ;;"Finds first interactive form in FUNCTION's redefining advices."
  (ad-dolist (advice (append (ad-get-enabled-advices function 'before)
			     (ad-get-enabled-advices function 'around)
			     (ad-get-enabled-advices function 'after)))
    (let ((interactive-form
	   (ad-interactive-form (ad-advice-definition advice))))
      (if interactive-form
	  ;; We found the first one, use it:
	  (ad-do-return interactive-form)))))

;; @@@ Putting it all together:
;; ============================

(defun ad-make-advised-definition (function)
  ;;"Generates an advised definition of FUNCTION from its advice info."
  (if (and (ad-is-advised function)
	   (ad-has-redefining-advice function))
      (let* ((origdef (ad-real-orig-definition function))
	     (origname (ad-get-advice-info-field function 'origname))
	     (orig-interactive-p (ad-interactive-p origdef))
	     (orig-subr-p (ad-subr-p origdef))
	     (orig-special-form-p (ad-special-form-p origdef))
	     (orig-macro-p (ad-macro-p origdef))
	     ;; Construct the individual pieces that we need for assembly:
	     (orig-arglist (ad-arglist origdef function))
	     (advised-arglist (or (ad-advised-arglist function)
				  orig-arglist))
	     (advised-interactive-form (ad-advised-interactive-form function))
	     (interactive-form
	      (cond (orig-macro-p nil)
		    (advised-interactive-form)
		    ((ad-interactive-form origdef))
		    ;; Otherwise we must have a subr: make it interactive if
		    ;; we have to and initialize required arguments in case
		    ;; it is called interactively:
		    (orig-interactive-p
		     (let ((reqargs (car (ad-parse-arglist advised-arglist))))
		       (if reqargs
			   (` (interactive
			       '(, (make-list (length reqargs) nil))))
			   '(interactive))))))
	     (orig-form
	      (cond ((or orig-special-form-p orig-macro-p)
		     ;; Special forms and macros will be advised into macros.
                     ;; The trick is to construct an expansion for the advised
		     ;; macro that does the correct thing when it gets eval'ed.
		     ;; For macros we'll just use the expansion of the original
		     ;; macro and return that. This way compiled advised macros
		     ;; will be expanded into something useful. Note that after
		     ;; advices have full control over whether they want to
		     ;; evaluate the expansion (the value of `ad-return-value')
		     ;; at macro expansion time or not. For special forms there
		     ;; is no solution that interacts reasonably with the
		     ;; compiler, hence we just evaluate the original at macro
		     ;; expansion time and return the result. The moral of that
		     ;; is that one should always deactivate advised special
		     ;; forms before one byte-compiles a file.
		     (` ((, (if orig-macro-p
				'macroexpand
			      'eval))
			 (cons '(, origname)
			       (, (ad-get-arguments advised-arglist 0))))))
		    ((and orig-subr-p
			  orig-interactive-p
			  (not advised-interactive-form))
		     ;; Check whether we were called interactively
		     ;; in order to do proper prompting:
		     (` (if (interactive-p)
			    (call-interactively '(, origname))
			  (, (ad-make-mapped-call
			      orig-arglist advised-arglist origname)))))
		    ;; And now for normal functions and non-interactive subrs
	            ;; (or subrs whose interactive behavior was advised):
		    (t (ad-make-mapped-call
			advised-arglist orig-arglist origname)))))

	;; Finally, build the sucker:
	(ad-assemble-advised-definition
	 (cond (orig-macro-p 'macro)
	       (orig-special-form-p 'special-form)
	       (t 'function))
	 advised-arglist
         (ad-make-advised-definition-docstring function)
	 interactive-form
	 orig-form
	 (ad-get-enabled-advices function 'before)
	 (ad-get-enabled-advices function 'around)
	 (ad-get-enabled-advices function 'after)))))

(defun ad-assemble-advised-definition
  (type args docstring interactive orig &optional befores arounds afters)

  ;;"Assembles an original and its advices into an advised function.
  ;;It constructs a function or macro definition according to TYPE which has to
  ;;be either `macro', `function' or `special-form'.  ARGS is the argument list
  ;;that has to be used, DOCSTRING if non-nil defines the documentation of the
  ;;definition, INTERACTIVE if non-nil is the interactive form to be used,
  ;;ORIG is a form that calls the body of the original unadvised function,
  ;;and BEFORES, AROUNDS and AFTERS are the lists of advices with which ORIG
  ;;should be modified.  The assembled function will be returned."

  (let (before-forms around-form around-form-protected after-forms definition)
    (ad-dolist (advice befores)
      (cond ((and (ad-advice-protected advice)
		  before-forms)
	     (setq before-forms
		   (` ((unwind-protect
			   (, (ad-prognify before-forms))
			 (,@ (ad-body-forms
			      (ad-advice-definition advice))))))))
	    (t (setq before-forms
		     (append before-forms
			     (ad-body-forms (ad-advice-definition advice)))))))

    (setq around-form (` (setq ad-return-value (, orig))))
    (ad-dolist (advice (reverse arounds))
      ;; If any of the around advices is protected then we
      ;; protect the complete around advice onion:
      (if (ad-advice-protected advice)
	  (setq around-form-protected t))
      (setq around-form
	    (ad-substitute-tree
	     (function (lambda (form) (eq form 'ad-do-it)))
	     (function (lambda (form) around-form))
	     (ad-prognify (ad-body-forms (ad-advice-definition advice))))))

    (setq after-forms
	  (if (and around-form-protected before-forms)
	      (` ((unwind-protect
		      (, (ad-prognify before-forms))
		    (, around-form))))
	    (append before-forms (list around-form))))
    (ad-dolist (advice afters)
      (cond ((and (ad-advice-protected advice)
		  after-forms)
	     (setq after-forms
		   (` ((unwind-protect
			   (, (ad-prognify after-forms))
			 (,@ (ad-body-forms
			      (ad-advice-definition advice))))))))
	    (t (setq after-forms
		     (append after-forms
			     (ad-body-forms (ad-advice-definition advice)))))))

    (setq definition
	  (` ((,@ (if (memq type '(macro special-form)) '(macro)))
	      lambda
	      (, args)
	      (,@ (if docstring (list docstring)))
	      (,@ (if interactive (list interactive)))
	      (let (ad-return-value)
		(,@ after-forms)
		(, (if (eq type 'special-form)
		       '(list 'quote ad-return-value)
		     'ad-return-value))))))

    (ad-insert-argument-access-forms definition args)))

;; This is needed for activation/deactivation hooks:
(defun ad-make-hook-form (function hook-name)
  ;;"Makes hook-form from FUNCTION's advice bodies in class HOOK-NAME."
  (let ((hook-forms
	 (mapcar (function (lambda (advice)
			     (ad-body-forms (ad-advice-definition advice))))
		 (ad-get-enabled-advices function hook-name))))
    (if hook-forms
	(ad-prognify (apply 'append hook-forms)))))


;; @@ Caching:
;; ===========
;; Generating an advised definition of a function is moderately expensive,
;; hence, it makes sense to cache it so we can reuse it in appropriate
;; circumstances.  Of course, it only makes sense to reuse a cached
;; definition if the current advice and function definition state is the
;; same as it was at the time when the cached definition was generated.
;; For that purpose we associate every cache with an id so we can verify
;; if it is still valid at a certain point in time.  This id mechanism
;; makes it possible to preactivate advised functions, write the compiled
;; advised definitions to a file and reuse them during the actual
;; activation without having to risk that the resulting definition will be
;; incorrect, well, almost.
;;
;; A cache id is a list with six elements:
;; 1) the list of names of enabled before advices
;; 2) the list of names of enabled around advices
;; 3) the list of names of enabled after advices
;; 4) the type of the original function (macro, subr, etc.)
;; 5) the arglist of the original definition (or t if it was equal to the
;;    arglist of the cached definition)
;; 6) t if the interactive form of the original definition was equal to the
;;    interactive form of the cached definition
;;
;; Here's how a cache can get invalidated or be incorrect:
;; A) a piece of advice used in the cache gets redefined
;; B) the current list of enabled advices is different from the ones used
;;    for the cache
;; C) the type of the original function changed, e.g., a function became a
;;    macro, or a subr became a function
;; D) the arglist of the original function changed
;; E) the interactive form of the original function changed
;; F) a piece of advice used in the cache got redefined before the
;;    defadvice with the cached definition got loaded: This is a PROBLEM!
;;
;; Cases A and B are the normal ones.  A is taken care of by `ad-add-advice'
;; which clears the cache in such a case, B is easily checked during
;; verification at activation time.
;;
;; Cases C, D and E have to be considered if one is slightly paranoid, i.e.,
;; if one considers the case that the original function could be different
;; from the one available at caching time (e.g., for forward advice of
;; functions that get redefined by some packages - such as `eval-region' gets
;; redefined by edebug).  All these cases can be easily checked during
;; verification.  Element 4 of the id lets one check case C, element 5 takes
;; care of case D (using t in the equality case saves some space, because the
;; arglist can be recovered at validation time from the cached definition),
;; and element 6 takes care of case E which is only a problem if the original
;; was actually a function whose interactive form was not overridden by a
;; piece of advice.
;;
;; Case F is the only one which will lead to an incorrect advised function.
;; There is no way to avoid this without storing the complete advice definition
;; in the cache-id which is not feasible.
;;
;; The cache-id of a typical advised function with one piece of advice and
;; no arglist redefinition takes 7 conses which is a small price to pay for
;; the added efficiency.  The validation itself is also pretty cheap, certainly
;; a lot cheaper than reconstructing an advised definition.

(defmacro ad-get-cache-definition (function)
  (` (car (ad-get-advice-info-field (, function) 'cache))))

(defmacro ad-get-cache-id (function)
  (` (cdr (ad-get-advice-info-field (, function) 'cache))))

(defmacro ad-set-cache (function definition id)
  (` (ad-set-advice-info-field
      (, function) 'cache (cons (, definition) (, id)))))

(defun ad-clear-cache (function)
  "Clears a previously cached advised definition of FUNCTION.
Clear the cache if you want to force `ad-activate' to construct a new
advised definition from scratch."
  (interactive
   (list (ad-read-advised-function "Clear cached definition of: ")))
  (ad-set-advice-info-field function 'cache nil))

(defun ad-make-cache-id (function)
  ;;"Generates an identifying image of the current advices of FUNCTION."
  (let ((original-definition (ad-real-orig-definition function))
	(cached-definition (ad-get-cache-definition function)))
    (list (mapcar (function (lambda (advice) (ad-advice-name advice)))
		  (ad-get-enabled-advices function 'before))
	  (mapcar (function (lambda (advice) (ad-advice-name advice)))
		  (ad-get-enabled-advices function 'around))
	  (mapcar (function (lambda (advice) (ad-advice-name advice)))
		  (ad-get-enabled-advices function 'after))
	  (ad-definition-type original-definition)
	  (if (equal (ad-arglist original-definition function)
		     (ad-arglist cached-definition))
	      t
	    (ad-arglist original-definition function))
	  (if (eq (ad-definition-type original-definition) 'function)
	      (equal (ad-interactive-form original-definition)
		     (ad-interactive-form cached-definition))))))

(defun ad-get-cache-class-id (function class)
  ;;"Returns the part of FUNCTION's cache id that identifies CLASS."
  (let ((cache-id (ad-get-cache-id function)))
    (if (eq class 'before)
	(car cache-id)
      (if (eq class 'around)
	  (nth 1 cache-id)
	(nth 2 cache-id)))))

(defun ad-verify-cache-class-id (cache-class-id advices)
  (ad-dolist (advice advices (null cache-class-id))
    (if (ad-advice-enabled advice)
	(if (eq (car cache-class-id) (ad-advice-name advice))
	    (setq cache-class-id (cdr cache-class-id))
	  (ad-do-return nil)))))

;; There should be a way to monitor if and why a cache verification failed
;; in order to determine whether a certain preactivation could be used or
;; not.  Right now the only way to find out is to trace 
;; `ad-cache-id-verification-code'.  The code it returns indicates where the
;; verification failed.  Tracing `ad-verify-cache-class-id' might provide
;; some additional useful information.

(defun ad-cache-id-verification-code (function)
  (let ((cache-id (ad-get-cache-id function))
	(code 'before-advice-mismatch))
    (and (ad-verify-cache-class-id
	  (car cache-id) (ad-get-advice-info-field function 'before))
	 (setq code 'around-advice-mismatch)
	 (ad-verify-cache-class-id
	  (nth 1 cache-id) (ad-get-advice-info-field function 'around))
	 (setq code 'after-advice-mismatch)
	 (ad-verify-cache-class-id
	  (nth 2 cache-id) (ad-get-advice-info-field function 'after))
	 (setq code 'definition-type-mismatch)
	 (let ((original-definition (ad-real-orig-definition function))
	       (cached-definition (ad-get-cache-definition function)))
	   (and (eq (nth 3 cache-id) (ad-definition-type original-definition))
		(setq code 'arglist-mismatch)
		(equal (if (eq (nth 4 cache-id) t)
			   (ad-arglist original-definition function)
			 (nth 4 cache-id) )
		       (ad-arglist cached-definition))
		(setq code 'interactive-form-mismatch)
		(or (null (nth 5 cache-id))
		    (equal (ad-interactive-form original-definition)
			   (ad-interactive-form cached-definition)))
		(setq code 'verified))))
    code))

(defun ad-verify-cache-id (function)
  ;;"True if FUNCTION's cache-id is compatible with its current advices."
  (eq (ad-cache-id-verification-code function) 'verified))


;; @@ Preactivation:
;; =================
;; Preactivation can be used to generate compiled advised definitions
;; at compile time without having to give up the dynamic runtime flexibility
;; of the advice mechanism.  Preactivation is a special feature of `defadvice',
;; it involves the following steps:
;;  - remembering the function's current state (definition and advice-info)
;;  - advising it with the defined piece of advice
;;  - clearing its cache
;;  - generating an interpreted advised definition by activating it, this will
;;    make use of all its current active advice and its current definition
;;  - saving the so generated cached definition and id
;;  - resetting the function's advice and definition state to what it was
;;    before the preactivation
;;  - Returning the saved definition and its id to be used in the expansion of
;;    `defadvice' to assign it as an initial cache, hence it will be compiled
;;    at time the `defadvice' gets compiled.
;; Naturally, for preactivation to be effective it has to be applied/compiled
;; at the right time, i.e., when the current state of advices and function
;; definition exactly reflects the state at activation time.  Should that not
;; be the case, the precompiled definition will just be discarded and a new
;; advised definition will be generated.

(defun ad-preactivate-advice (function advice class position)
  ;;"Preactivates FUNCTION and returns the constructed cache."
  (let* ((function-defined-p (fboundp function))
	 (old-definition
	  (if function-defined-p
	      (symbol-function function)))
	 (old-advice-info (ad-copy-advice-info function))
	 (ad-advised-functions ad-advised-functions))
    (unwind-protect
	(progn
	  (ad-add-advice function advice class position)
	  (ad-enable-advice function class (ad-advice-name advice))
	  (ad-clear-cache function)
	  (ad-activate function nil)
	  (if (and (ad-is-active function)
	           (ad-get-cache-definition function))
	      (list (ad-get-cache-definition function)
		    (ad-get-cache-id function))))
      (ad-set-advice-info function old-advice-info)
      ;; Don't `fset' function to nil if it was previously unbound:
      (if function-defined-p
	  (ad-real-fset function old-definition)
	(fmakunbound function)))))

(defun ad-activate-advised-definition (function compile)
  ;;"Redefines FUNCTION with its advised definition from cache or scratch.
  ;;If COMPILE is true the resulting FUNCTION will be compiled.  The current
  ;;definition and its cache-id will be put into the cache."
  (let ((verified-cached-definition
	 (if (ad-verify-cache-id function)
	     (ad-get-cache-definition function))))
    (ad-real-fset function
		  (or verified-cached-definition
		      (ad-make-advised-definition function)))
    (if compile (ad-compile-function function))
    (if verified-cached-definition
	(if (not (eq verified-cached-definition (symbol-function function)))
	    ;; we must have compiled, cache the compiled definition:
	    (ad-set-cache
	     function (symbol-function function) (ad-get-cache-id function)))
      ;; We created a new advised definition, cache it with a proper id:
      (ad-clear-cache function)
      ;; ad-make-cache-id needs the new cached definition:
      (ad-set-cache function (symbol-function function) nil)
      (ad-set-cache
       function (symbol-function function) (ad-make-cache-id function)))))

(defun ad-handle-definition (function)
  "Handles re/definition of an advised FUNCTION during de/activation.
If FUNCTION does not have an original definition associated with it and
the current definition is usable, then it will be stored as FUNCTION's
original definition.  If no current definition is available (even in the
case of undefinition) nothing will be done.  In the case of redefinition
the action taken depends on the value of `ad-redefinition-action' (which
see).  Redefinition occurs when FUNCTION already has an original definition
associated with it but got redefined with a new definition and then
de/activated.  If you do not like the current redefinition action change
the value of `ad-redefinition-action' and de/activate again."
  (let ((original-definition (ad-get-orig-definition function))
	(current-definition (if (ad-real-definition function)
				(symbol-function function))))
    (if original-definition
	(if current-definition
	    (if (and (not (eq current-definition original-definition))
		     ;; Redefinition with an advised definition from a
		     ;; different function won't count as such:
		     (not (ad-advised-definition-p current-definition)))
		;; we have a redefinition:
		(if (not (memq ad-redefinition-action '(accept discard warn)))
		    (error "ad-handle-definition (see its doc): `%s' %s"
			   function "illegally redefined")
		  (if (eq ad-redefinition-action 'discard)
		      (ad-real-fset function original-definition)
		    (ad-set-orig-definition function current-definition)
		    (if (eq ad-redefinition-action 'warn)
			(message "ad-handle-definition: `%s' got redefined"
				 function))))
	      ;; either advised def or correct original is in place:
	      nil)
	  ;; we have an undefinition, ignore it:
	  nil)
      (if current-definition
	  ;; we have a first definition, save it as original:
	  (ad-set-orig-definition function current-definition)
	;; we don't have anything noteworthy:
	nil))))


;; @@ The top-level advice interface:
;; ==================================

(defun ad-activate (function &optional compile)
  "Activates all the advice information of an advised FUNCTION.
If FUNCTION has a proper original definition then an advised
definition will be generated from FUNCTION's advice info and the
definition of FUNCTION will be replaced with it.  If a previously
cached advised definition was available, it will be used.  With an
argument (COMPILE is non-nil) the resulting function (or a compilable
cached definition) will also be compiled.  Activation of an advised
function that has an advice info but no actual pieces of advice is
equivalent to a call to `ad-unadvise'.  Activation of an advised
function that has actual pieces of advice but none of them are enabled
is equivalent to a call to `ad-deactivate'.  The current advised
definition will always be cached for later usage."
  (interactive
   (list (ad-read-advised-function "Activate advice of: ")
	 current-prefix-arg))
  (if (not (ad-is-advised function))
      (error "ad-activate: `%s' is not advised" function)
    (ad-handle-definition function)
    ;; Just return for forward advised and not yet defined functions:
    (if (ad-get-orig-definition function)
	(if (not (ad-has-any-advice function))
	    (ad-unadvise function)
	  ;; Otherwise activate the advice:
	  (cond ((ad-has-redefining-advice function)
		 (ad-activate-advised-definition function compile)
		 (ad-set-advice-info-field function 'active t)
		 (eval (ad-make-hook-form function 'activation))
		 function)
		;; Here we are if we have all disabled advices:
		(t (ad-deactivate function)))))))

(defun ad-deactivate (function)
  "Deactivates the advice of an actively advised FUNCTION.
If FUNCTION has a proper original definition, then the current
definition of FUNCTION will be replaced with it.  All the advice
information will still be available so it can be activated again with
a call to `ad-activate'."
  (interactive
   (list (ad-read-advised-function "Deactivate advice of: " 'ad-is-active)))
  (if (not (ad-is-advised function))
      (error "ad-deactivate: `%s' is not advised" function)
    (cond ((ad-is-active function)
	   (ad-handle-definition function)
	   (if (not (ad-get-orig-definition function))
	       (error "ad-deactivate: `%s' has no original definition"
		      function)
	     (ad-real-fset function (ad-get-orig-definition function))
	     (ad-set-advice-info-field function 'active nil)
	     (eval (ad-make-hook-form function 'deactivation))
	     function)))))

(defun ad-update (function &optional compile)
  "Update the advised definition of FUNCTION if its advice is active.
With a prefix argument or if the current definition is compiled compile the 
resulting advised definition."
  (interactive
   (list (ad-read-advised-function
	  "Update advised definition of: " 'ad-is-active)))
  (if (ad-is-active function)
      (ad-activate
       function (or compile (ad-compiled-p (symbol-function function))))))

(defun ad-unadvise (function)
  "Deactivates FUNCTION and then removes all its advice information. 
If FUNCTION was not advised this will be a noop."
  (interactive
   (list (ad-read-advised-function "Unadvise function: ")))
  (cond ((ad-is-advised function)
	 (if (ad-is-active function)
	     (ad-deactivate function))
	 (ad-clear-orig-definition function)
	 (ad-set-advice-info function nil)
	 (ad-pop-advised-function function))))

(defun ad-recover (function)
  "Tries to recover FUNCTION's original definition and unadvises it.
This is more low-level than `ad-unadvise' because it does not do any
deactivation which might run hooks and get into other trouble.
Use in emergencies."
  ;; Use more primitive interactive behavior here: Accept any symbol that's
  ;; currently defined in obarray, not necessarily with a function definition:
  (interactive
   (list (intern
	  (completing-read "Recover advised function: " obarray nil t))))
  (cond ((ad-is-advised function)
	 (cond ((ad-get-orig-definition function)
	        (ad-real-fset function (ad-get-orig-definition function))
		(ad-clear-orig-definition function)))
	 (ad-set-advice-info function nil)
	 (ad-pop-advised-function function))))

(defun ad-activate-regexp (regexp &optional compile)
  "Activates functions with an advice name containing a REGEXP match.
With prefix argument compiles resulting advised definitions."
  (interactive
   (list (ad-read-regexp "Activate via advice regexp: ")
	 current-prefix-arg))
  (ad-do-advised-functions (function)
    (if (ad-find-some-advice function 'any regexp)
	(ad-activate function compile))))

(defun ad-deactivate-regexp (regexp)
  "Deactivates functions with an advice name containing REGEXP match."
  (interactive
   (list (ad-read-regexp "Deactivate via advice regexp: ")))
  (ad-do-advised-functions (function)
    (if (ad-find-some-advice function 'any regexp)
	(ad-deactivate function))))

(defun ad-update-regexp (regexp &optional compile)
  "Updates functions with an advice name containing a REGEXP match.
With prefix argument compiles resulting advised definitions."
  (interactive
   (list (ad-read-regexp "Update via advice regexp: ")
	 current-prefix-arg))
  (ad-do-advised-functions (function)
    (if (ad-find-some-advice function 'any regexp)
	(ad-update function compile))))

(defun ad-activate-all (&optional compile)
  "Activates all currently advised functions.
With prefix argument compiles resulting advised definitions."
  (interactive "P")
  (ad-do-advised-functions (function)
    (ad-activate function)))

(defun ad-deactivate-all ()
  "Deactivates all currently advised functions."
  (interactive)
  (ad-do-advised-functions (function)
    (ad-deactivate function)))

(defun ad-update-all (&optional compile)
  "Updates all currently advised functions.
With prefix argument compiles resulting advised definitions."
  (interactive "P")
  (ad-do-advised-functions (function)
    (ad-update function compile)))

(defun ad-unadvise-all ()
  "Unadvises all currently advised functions."
  (interactive)
  (ad-do-advised-functions (function)
    (ad-unadvise function)))

(defun ad-recover-all ()
  "Recovers all currently advised functions.  Use in emergencies."
  (interactive)
  (ad-do-advised-functions (function)
    (condition-case nil
	(ad-recover function)
      (error nil))))


;; Completion alist of legal `defadvice' flags
(defvar ad-defadvice-flags
  '(("protect") ("disable") ("activate")
    ("compile") ("preactivate") ("freeze")))

;;;###autoload
(defmacro defadvice (function args &rest body)
  "Defines a piece of advice for FUNCTION (a symbol).
The syntax of `defadvice' is as follows:

  (defadvice FUNCTION (CLASS NAME [POSITION] [ARGLIST] FLAG...)
    [DOCSTRING] [INTERACTIVE-FORM]
    BODY... )

FUNCTION ::= Name of the function to be advised.
CLASS ::= `before' | `around' | `after' | `activation' | `deactivation'.
NAME ::= Non-nil symbol that names this piece of advice.
POSITION ::= `first' | `last' | NUMBER. Optional, defaults to `first',
    see also `ad-add-advice'.
ARGLIST ::= An optional argument list to be used for the advised function
    instead of the argument list of the original.  The first one found in
    before/around/after-advices will be used.
FLAG ::= `protect'|`disable'|`activate'|`compile'|`preactivate'|`freeze'.
    All flags can be specified with unambiguous initial substrings.
DOCSTRING ::= Optional documentation for this piece of advice.
INTERACTIVE-FORM ::= Optional interactive form to be used for the advised
    function.  The first one found in before/around/after-advices will be used.
BODY ::= Any s-expression.

Semantics of the various flags:
`protect': The piece of advice will be protected against non-local exits in
any code that precedes it.  If any around-advice of a function is protected
then automatically all around-advices will be protected (the complete onion).

`activate': All advice of FUNCTION will be activated immediately if
FUNCTION has been properly defined prior to this application of `defadvice'.

`compile': In conjunction with `activate' specifies that the resulting
advised function should be compiled.

`disable': The defined advice will be disabled, hence, it will not be used 
during activation until somebody enables it.

`preactivate': Preactivates the advised FUNCTION at macro-expansion/compile
time.  This generates a compiled advised definition according to the current
advice state that will be used during activation if appropriate.  Only use
this if the `defadvice' gets actually compiled.

`freeze': Expands the `defadvice' into a redefining `defun/defmacro' according
to the current advice state.  No other advice information will be saved.
Frozen advices cannot be undone, they behave like a hard redefinition of
the advised function.  `freeze' implies `activate' and `preactivate'.  The
documentation of the advised function can be dumped onto the `DOC' file
during preloading.

Look at the file `advice.el' for comprehensive documentation."
  (if (not (ad-name-p function))
      (error "defadvice: Illegal function name: %s" function))
  (let* ((class (car args))
	 (name (if (not (ad-class-p class))
		   (error "defadvice: Illegal advice class: %s" class)
		 (nth 1 args)))
	 (position (if (not (ad-name-p name))
		       (error "defadvice: Illegal advice name: %s" name)
		     (setq args (nthcdr 2 args))
		     (if (ad-position-p (car args))
			 (prog1 (car args)
			   (setq args (cdr args))))))
	 (arglist (if (listp (car args))
		      (prog1 (car args)
			(setq args (cdr args)))))
	 (flags
	  (mapcar
	   (function
	    (lambda (flag)
	      (let ((completion
		     (try-completion (symbol-name flag) ad-defadvice-flags)))
		(cond ((eq completion t) flag)
		      ((assoc completion ad-defadvice-flags)
		       (intern completion))
		      (t (error "defadvice: Illegal or ambiguous flag: %s"
				flag))))))
	   args))
	 (advice (ad-make-advice
		  name (memq 'protect flags)
		  (not (memq 'disable flags))
		  (` (advice lambda (, arglist) (,@ body)))))
	 (preactivation (if (memq 'preactivate flags)
			    (ad-preactivate-advice
			     function advice class position)))
	 unique-origname
	 (redefinition
	  (if (memq 'freeze flags)
	      (ad-with-originals (ad-make-advised-definition-docstring
				  ad-make-origname)
		;; Make sure we construct the actual docstring:
		(fset 'ad-make-advised-definition-docstring
		      'ad-make-freeze-docstring)
		;; With a unique origname we can have multiple freeze advices
		;; for the same function, each overloading the previous one:
		(setq unique-origname
		      (intern (format "%s-%s-%s"
				      (ad-make-origname function) class name)))
		(fset 'ad-make-origname '(lambda (x) unique-origname))
		(if (not (ad-has-proper-definition function))
		    (error
		     "defadvice: `freeze' needs proper definition of `%s'"
		     function))
		(ad-preactivate-advice function advice class position)))))
    ;; Now for the things to be done at evaluation time:
    (if redefinition
	;; jwz's idea: Freeze the advised definition into a dumpable
	;; defun/defmacro whose docs can be written to the DOC file:
	(let* ((macro-p (ad-macro-p (car redefinition)))
	       (body (cdr (if macro-p
			      (ad-lambdafy (car redefinition))
			    (car redefinition)))))
	  (` (progn
	       (if (not (fboundp '(, unique-origname)))
		   (fset '(, unique-origname) (symbol-function '(, function))))
	       ((, (if macro-p 'defmacro 'defun))
		(, function)
		(,@ body)))))
      ;; the normal case:	 
      (` (progn
	   (ad-add-advice '(, function) '(, advice) '(, class) '(, position))
	   (,@ (if preactivation
		   (` ((ad-set-cache
			'(, function)
			;; the function will get compiled:
			(, (cond ((ad-macro-p (car preactivation))
				  (` (ad-macrofy
				      (function
				       (, (ad-lambdafy
					   (car preactivation)))))))
				 (t (` (function
					(, (car preactivation)))))))
			'(, (car (cdr preactivation))))))))
	   (,@ (if (memq 'activate flags)
		   (` ((ad-activate '(, function)
				    (, (if (memq 'compile flags) t)))))))
	   '(, function))))))


;; @@ Tools:
;; =========

(defmacro ad-with-originals (functions &rest body)
  "Binds FUNCTIONS to their original definitions and executes BODY.
For any members of FUNCTIONS that are not currently advised the rebinding will
be a noop.  Any modifications done to the definitions of FUNCTIONS will be
undone on exit of this macro."
  (let* ((index -1)
	 ;; Make let-variables to store current definitions:
	 (current-bindings
	  (mapcar (function
		   (lambda (function)
		     (setq index (1+ index))
		     (list (intern (format "ad-oRiGdEf-%d" index))
			   (` (symbol-function '(, function))))))
		  functions)))
    (` (let (, current-bindings)
	 (unwind-protect
	     (progn
	       (,@ (progn
		     ;; Make forms to redefine functions to their
		     ;; original definitions if they are advised:
		     (setq index -1)
		     (mapcar
		      (function
		       (lambda (function)
			 (setq index (1+ index))
			 (` (ad-real-fset
			     '(, function)
			     (or (ad-get-orig-definition '(, function))
				 (, (car (nth index current-bindings))))))))
		      functions)))
	       (,@ body))
	   (,@ (progn
		 ;; Make forms to back-define functions to the definitions
		 ;; they had outside this macro call:
		 (setq index -1)
		 (mapcar
		  (function
		   (lambda (function)
		     (setq index (1+ index))
		     (` (ad-real-fset
			 '(, function)
			 (, (car (nth index current-bindings)))))))
		  functions))))))))

(if (not (get 'ad-with-originals 'lisp-indent-hook))
    (put 'ad-with-originals 'lisp-indent-hook 1))


;; @@ Advising `defun', `defmacro', `fset' and `documentation'
;; ===========================================================
;; Use the advice mechanism to advise defun/defmacro/fset so we can forward
;; advise functions that might be defined later during load/autoload. 
;; Enabling forward advice was the original motivation for doing this, it
;; has now been generalized to running definition hooks so other packages
;; can make use of this sort of functionality too.

(defvar ad-defined-function nil)

(defun ad-activate-defined-function (&optional function)
  "Activates the advice of an advised and defined FUNCTION.
If the current definition of FUNCTION is byte-compiled then the advised
definition will be compiled too.  FUNCTION defaults to the value of
`ad-defined-function'."
  (if (and (null function)
	   ad-defined-function)
      (setq function ad-defined-function))
  (if (and (ad-is-advised function)
	   (ad-real-definition function))
      (ad-activate function (ad-compiled-p (symbol-function function)))))

(defvar ad-advised-definers
  '(defun defmacro fset defalias define-function))

(defadvice defun (after ad-definition-hooks first disable preact)
  "Whenever a function gets re/defined with `defun' all hook functions
in `ad-definition-hooks' will be run after the re/definition with
`ad-defined-function' bound to the name of the function."
  (let ((ad-defined-function (ad-get-arg 0)))
    (run-hooks 'ad-definition-hooks)))

(defadvice defmacro (after ad-definition-hooks first disable preact)
  "Whenever a macro gets re/defined with `defmacro' all hook functions
in `ad-definition-hooks' will be run after the re/definition with
`ad-defined-function' bound to the name of the function."
  (let ((ad-defined-function (ad-get-arg 0)))
    (run-hooks 'ad-definition-hooks)))

(defadvice fset (after ad-definition-hooks first disable preact)
  "Whenever a function gets re/defined with `fset' all hook functions
in `ad-definition-hooks' will be run after the re/definition with
`ad-defined-function' bound to the name of the function.  This advice was
mainly created to handle forward-advice for byte-compiled files created
by jwz's byte-compiler used in Lemacs.
CAUTION: If you need the primitive `fset' behavior either deactivate
         its advice or use `ad-real-fset' instead!"
  (let ((ad-defined-function (ad-get-arg 0)))
    (run-hooks 'ad-definition-hooks)))

;; In Lemacs this is just a noop:
(defadvice defalias (after ad-definition-hooks first disable preact)
  "Whenever a function gets re/defined with `defalias' all hook functions
in `ad-definition-hooks' will be run after the re/definition with
`ad-defined-function' bound to the name of the function."
  (let ((ad-defined-function (ad-get-arg 0)))
    ;; The new `byte-compile' uses `defalias' to set the definition which
    ;; leads to infinite recursion if it gets to use the advised version
    ;; (with `fset' this didn't matter because the compiled `byte-compile'
    ;; called it via its byte-code).  Should there be a general provision to
    ;; avoid recursive application of definition hooks?
    (ad-with-originals (defalias)
      (run-hooks 'ad-definition-hooks))))

;; Needed for Emacs (seems to be an identical copy of `defalias', but
;; it is used in `simple.el' and might be used later, hence, advise it):
(defadvice define-function (after ad-definition-hooks first disable preact)
  "Whenever a function gets re/defined with `define-function' all hook
functions in `ad-definition-hooks' will be run after the re/definition with
`ad-defined-function' bound to the name of the function."
  (let ((ad-defined-function (ad-get-arg 0)))
    (ad-with-originals (define-function)
      (run-hooks 'ad-definition-hooks))))

(defadvice documentation (after ad-advised-docstring first disable preact)
  "Builds an advised docstring if FUNCTION is advised."
  ;; Because we get the function name from the advised docstring
  ;; this will work for function names as well as for definitions:
  (if (and (stringp ad-return-value)
	   (string-match
	    ad-advised-definition-docstring-regexp ad-return-value))
      (let ((function
	     (car (read-from-string
		   ad-return-value (match-beginning 1) (match-end 1)))))
	(cond ((ad-is-advised function)
	       (setq ad-return-value (ad-make-advised-docstring function))
	       ;; Handle optional `raw' argument: 
	       (if (not (ad-get-arg 1))
		   (setq ad-return-value
			 (substitute-command-keys ad-return-value))))))))

;; The following two advised functions are a (hopefully temporary) kludge
;; to fix a problem with the compilation of embedded (or non-top-level)
;; `defun/defmacro's when automatic activation of advice is enabled.  For
;; the time of the compilation they backdefine `defun/defmacro' to their
;; original definition to make sure they are not treated as plain macros.
;; Both advices are forward advices, hence, they will only be activated if
;; automatic advice activation is enabled, but since that is the actual
;; situation where we have a problem, we can be sure that the advices will 
;; be active when we need them.

;; We only need this in Lemacs, because in Emacs it is
;; now taken care of directly by the byte-compiler:
(cond ((ad-lemacs-p)

(defvar ad-advised-byte-compilers
  '(byte-compile-from-buffer byte-compile-top-level))

(defadvice byte-compile-from-buffer (around ad-deactivate-defun-defmacro
					    first disable preact)
  "Deactivates `defun/defmacro' for proper compilation when they are embedded."
  (let (;; make sure no `require' starts them again by accident:
	(ad-advised-definers '(fset defalias define-function)))
    (ad-with-originals (defun defmacro)
      ad-do-it)))

(defadvice byte-compile-top-level (around ad-deactivate-defun-defmacro
					  first disable preact)
  "Deactivates `defun/defmacro' for proper compilation when they are embedded."
  (let (;; make sure no `require' starts them again by accident:
	(ad-advised-definers '(fset defalias define-function)))
    (ad-with-originals (defun defmacro)
      ad-do-it)))

)) ;; end of cond

;; Make sure advice-infos are not allocated in pure space 
;; (this might not be necessary anymore):
(ad-dolist (advised-function (cons 'documentation
				   (append ad-advised-definers
					   (if (ad-lemacs-p)
					       ad-advised-byte-compilers))))
  (ad-set-advice-info advised-function (ad-copy-advice-info advised-function)))


;; @@ Forward advice support for jwz's byte-compiler (M-x serious-HACK-mode-on)
;; ============================================================================
;; Jamie Zawinski's optimizing byte-compiler used in v19 (and by some daring
;; folks in v18) produces compiled files that do not define functions via
;; explicit calls to `defun/defmacro', it rather uses `fset' for functions with
;; documentation strings, and hunks of byte-code for sets of functions without
;; any documentation.  In Jamie's byte-compiler a series of compiled functions
;; without docstrings get hunked as 
;;     (progn (fset 'f1 <code1>) (fset 'f2 <code2>) ...).
;; The resulting progn will be compiled and the compiled form will be written
;; to the compiled file as `(byte-code [progn-code] [constants] [depth])'.  To
;; handle forward advice we have to know when functions get defined so we can
;; activate any advice there might be.  For standard v18 byte-compiled files
;; we can do this by simply advising `defun/defmacro' because these subrs are
;; evaluated explicitly when such a file is loaded.  For Jamie's v19 compiler
;; our only choice is to additionally advise `fset' and change the subr
;; `byte-code' such that it analyzes its byte-code string looking for fset's
;; when we are currently loading a file.  In v19 the general overhead caused
;; by the advice of `byte-code' shouldn't be too bad, because byte-compiled
;; functions do not call byte-code explicitly (as done in v18).  In v18 this
;; is a problem because with the changed `byte-code' function function calls
;; become more expensive. 
;;
;; Wish-List: 
;;  - special defining functions for use in byte-compiled files, e.g., 
;;    `byte-compile-fset' and `byte-code-tl' which do the same as their
;;    standard brothers, but which can be advised for forward advice without
;;    the problems that advising `byte-code' generates.
;;  - More generally, a symbol definition hook that could be used for 
;;    forward advice and related purposes.
;;
;; Until then: For the analysis of the byte-code string we simply scan it for
;; an `fset' opcode (M in ascii) that is preceded by two constant references,
;; the first of which points to the function name and the second to its code.
;; A constant reference can either be a simple one-byte one, or a three-byte
;; one if the function has more than 64 constants.  The scanning can pretty
;; efficiently be done with a regular expression.  Here it goes:

;; Have to hardcode these opcodes if I don't
;; want to require the byte-compiler:
(defvar byte-constant 192)
(defvar byte-constant-limit 64)
(defvar byte-constant2 129)
(defvar byte-fset 77)

;; Matches a byte-compiled fset operation with two constant arguments:
(defvar ad-byte-code-fset-regexp
  (let* ((constant-reference
	  (format "[%s-%s]"
		  (char-to-string byte-constant)
		  (char-to-string (+ byte-constant (1- byte-constant-limit)))))
	 (constant2-reference
	  ;; \0 makes it necessary to use concat instead of format in 18.57:
	  (concat (char-to-string byte-constant2) "[\0-\377][\0-\377]"))
	 (fset-opcode (char-to-string byte-fset)))
    (concat "\\(" constant-reference "\\|" constant2-reference "\\)"
	    "\\(" constant-reference "\\|" constant2-reference "\\)"
	    fset-opcode)))

(defun ad-find-fset-in-byte-code (code constants start)
  ;;"Finds the first two-constant fset operation in CODE after START.
  ;;Returns a three element list consisting of the name of the defined 
  ;;function, its code (both taken from the CONSTANTS vector), and an
  ;;advanced start index."
  (let ((start
	 ;; The odd case that this regexp matches something that isn't an
	 ;; actual fset operation is handled by additional tests and a
	 ;; condition handler in ad-scan-byte-code-for-fsets:
	 (string-match ad-byte-code-fset-regexp code start))
	name-index code-index)
    (cond (start
	   (cond ((= (aref code start) byte-constant2)
		  (setq name-index
			(+ (aref code (setq start (1+ start)))
			   (* (aref code (setq start (1+ start))) 256)))
		  (setq start (1+ start)))
		 (t (setq name-index (- (aref code start) byte-constant))
		    (setq start (1+ start))))
	   (cond ((= (aref code start) byte-constant2)
		  (setq code-index
			(+ (aref code (setq start (1+ start)))
			   (* (aref code (setq start (1+ start))) 256)))
		  (setq start (1+ start)))
		 (t (setq code-index (- (aref code start) byte-constant))
		    (setq start (1+ start))))
	   (list (aref constants name-index)
		 (aref constants code-index)
		 ;; start points to fset opcode:
		 start))
	  (t nil))))

(defun ad-scan-byte-code-for-fsets (ad-code ad-constants)
  ;; In case anything in here goes wrong we reset `byte-code' to its real
  ;; identity.  In particular, the handler of the condition-case uses
  ;; `byte-code', so it better be the real one if we have an error:
  (ad-real-fset 'byte-code (symbol-function 'ad-real-byte-code))
  (condition-case nil
      (let ((fset-args '(0 0 0)))
	(while (setq fset-args (ad-find-fset-in-byte-code
				ad-code ad-constants
				(car (cdr (cdr fset-args)))))
	  (if (and (symbolp (car fset-args))
		   (fboundp (car fset-args))
		   (eq (symbol-function (car fset-args))
		       (car (cdr fset-args))))
	      ;; We've found an fset that was executed during this call
	      ;; to byte-code, and whose definition is still eq to the
	      ;; current definition of the defined function:
	      (let ((ad-defined-function (car fset-args)))
		(run-hooks 'ad-definition-hooks))))
	;; Everything worked fine, readvise `byte-code':
	(ad-real-fset 'byte-code (symbol-function 'ad-advised-byte-code)))
    (error nil)))

;; CAUTION: Don't try this at home!! Changing `byte-code' is a 
;;          pretty suicidal activity.
;; To allow v19 forward advice we cannot advise `byte-code' as a subr as
;; we did for `defun' etc., because `ad-subr-args' of the advised
;; `byte-code' would shield references to `ad-subr-args' in the body of
;; v18 compiled advised subrs such as `defun', and, more importantly, the
;; changed version of `byte-code' has to be as small and efficient as
;; possible because it is used in every call to a compiled function.
;; Hence, we previously saved its original definition and redefine it as
;; the following function - yuck:

;; The arguments will scope around the body of every byte-compiled
;; function, hence they have to be obscure enough to not be equal to any
;; global or argument variable referenced by any compiled function:
(defun ad-advised-byte-code (ad-cOdE ad-cOnStAnTs ad-dEpTh)
  "Modified version of `byte-code' subr used by the Advice package.
`byte-code' has been modified to allow automatic activation of forward
advice for functions that are defined in byte-compiled files.
See `ad-real-byte-code' for original documentation."
  (prog1 (ad-real-byte-code ad-cOdE ad-cOnStAnTs ad-dEpTh)
    (if load-in-progress
	(ad-scan-byte-code-for-fsets ad-cOdE ad-cOnStAnTs))))

(defun ad-recover-byte-code ()
  "Recovers the real `byte-code' functionality."
  (interactive)
  (ad-real-fset 'byte-code (symbol-function 'ad-real-byte-code)))

(defun ad-enable-definition-hooks ()
  ;;"Enables definition hooks by redefining definition primitives.
  ;;Activates the advice of defun/defmacro/fset and redefines `byte-code'.
  ;;Redefining these primitives might lead to problems.  Use
  ;;`ad-disable-definition-hooks' or `ad-stop-advice' in such a case
  ;;to establish a safe state."
  (ad-dolist (definer ad-advised-definers)
    (ad-enable-advice definer 'after 'ad-definition-hooks)
    (ad-activate definer 'compile))
  (if (ad-lemacs-p)
      (ad-dolist (byte-compiler ad-advised-byte-compilers)
	(ad-enable-advice byte-compiler 'around 'ad-deactivate-defun-defmacro)
	(ad-activate byte-compiler 'compile)))
  ;; Now redefine byte-code...
  (ad-real-fset 'byte-code (symbol-function 'ad-advised-byte-code)))

(defun ad-disable-definition-hooks ()
  ;;"Disables definition hooks by resetting definition primitives."
  (ad-recover-byte-code)
  (ad-dolist (definer ad-advised-definers)
    (ad-disable-advice definer 'after 'ad-definition-hooks)
    (ad-update definer))
  (if (ad-lemacs-p)
      (ad-dolist (byte-compiler ad-advised-byte-compilers)
	(ad-disable-advice byte-compiler 'around 'ad-deactivate-defun-defmacro)
	(ad-update byte-compiler 'compile))))


;; @@ Starting, stopping and recovering from the advice package magic:
;; ===================================================================

;;;###autoload
(defun ad-start-advice ()
  "Redefines some primitives to start the advice magic.
If `ad-activate-on-definition' is t then advice information will
automatically get activated whenever an advised function gets defined or
redefined.  This will enable goodies such as forward advice and
automatically enable function definition hooks.  If its value is nil but
the value of `ad-enable-definition-hooks' is t then definition hooks
will be enabled without having automatic advice activation, otherwise
function definition hooks will be disabled too.  If definition hooks are
enabled then functions stored in `ad-definition-hooks' are run whenever
a function gets defined or redefined."
  (interactive)
  (ad-enable-advice 'documentation 'after 'ad-advised-docstring)
  (ad-activate 'documentation 'compile)
  (if (or ad-activate-on-definition
	  ad-enable-definition-hooks)
      (ad-enable-definition-hooks)
    (ad-disable-definition-hooks))
  (setq ad-definition-hooks
	(if ad-activate-on-definition
	    (if (memq 'ad-activate-defined-function ad-definition-hooks)
		ad-definition-hooks
	      (cons 'ad-activate-defined-function ad-definition-hooks))
	  (delq 'ad-activate-defined-function ad-definition-hooks))))

(defun ad-stop-advice ()
  "Undefines some primitives to stop the advice magic.
This can also be used to recover from advice related emergencies."
  (interactive)
  (ad-recover-byte-code)
  (ad-disable-advice 'documentation 'after 'ad-advised-docstring)
  (ad-update 'documentation)
  (ad-disable-definition-hooks)
  (setq ad-definition-hooks
	(delq 'ad-activate-defined-function ad-definition-hooks)))

(defun ad-recover-normality ()
  "Undoes all advice related redefinitions and unadvises everything. 
Use only in REAL emergencies."
  (interactive)
  (ad-recover-byte-code)
  (ad-recover-all)
  (setq ad-advised-functions nil))

(if (and ad-start-advice-on-load
         ;; ...but only if we are compiled:
	 (ad-compiled-p (symbol-function 'ad-start-advice)))
    (ad-start-advice))

(provide 'advice)

;;; advice.el ends here