From: Stefan Monnier Date: Tue, 18 Mar 2014 01:51:12 +0000 (-0400) Subject: * doc/lispref/functions.texi (Advising Functions): Try and improve the text. X-Git-Tag: emacs-24.3.90~163 X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=6c187ef5a510d493bf74de04da2b3a80e944c5e6;p=emacs.git * doc/lispref/functions.texi (Advising Functions): Try and improve the text. Add example use of advice-add. (Core Advising Primitives): Rename. Explain handling of interactive specs, including advice-eval-interactive-spec. (Advising Named Functions): Try and better explain the difference with add-function. (Porting old advices): New node. Fixes: debbugs:16959 --- diff --git a/doc/lispref/ChangeLog b/doc/lispref/ChangeLog index 37531b0fb31..35ad6e86de9 100644 --- a/doc/lispref/ChangeLog +++ b/doc/lispref/ChangeLog @@ -1,3 +1,13 @@ +2014-03-18 Stefan + + * functions.texi (Advising Functions): Try and improve the text. + Add example use of advice-add (bug#16959). + (Core Advising Primitives): Rename. Explain handling of interactive + specs, including advice-eval-interactive-spec. + (Advising Named Functions): Try and better explain the difference with + add-function. + (Porting old advices): New node. + 2014-03-18 Paul Eggert Style fixes for floating-point doc. @@ -16,8 +26,7 @@ * display.texi (Temporary Displays): Rewrite descriptions of `with-output-to-temp-buffer' and `with-temp-buffer-window'. - * help.texi (Help Functions): Rewrite description of - `with-help-window'. + * help.texi (Help Functions): Rewrite description of `with-help-window'. 2014-03-15 Dmitry Gutov @@ -34,12 +43,10 @@ 2014-03-09 Martin Rudalics - * elisp.texi (Top): Rename section "Width" to "Size of Displayed - Text". + * elisp.texi (Top): Rename section "Width" to "Size of Displayed Text". * text.texi (Primitive Indent): * strings.texi (String Basics): - * sequences.texi (Sequence Functions): Update references - accordingly. + * sequences.texi (Sequence Functions): Update references accordingly. * display.texi (Size of Displayed Text): Rename section from "Width". Add description for `window-text-pixel-size'. (Window Dividers): Reword description of window dividers. @@ -64,12 +71,12 @@ 2014-03-06 Martin Rudalics * frames.texi (Size and Position): Rewrite entries for - `fit-frame-to-buffer' and `fit-frame-to-buffer-margins'. Add - description for `fit-frame-to-buffer-sizes'. + `fit-frame-to-buffer' and `fit-frame-to-buffer-margins'. + Add description for `fit-frame-to-buffer-sizes'. * windows.texi (Resizing Windows): Add descriptions for pixelwise resizing. Add entries for `window-resize-pixelwise' - and `fit-window-to-buffer-horizontally'. Rewrite - `fit-window-to-buffer' entry. + and `fit-window-to-buffer-horizontally'. + Rewrite `fit-window-to-buffer' entry. 2014-03-06 Xue Fuqiao @@ -93,8 +100,7 @@ `window-min-height' and `window-min-width'. Remove description of `window-size-fixed-p' moving part of it to that of `window-size-fixed'. - (Resizing Windows): Mention dividers when talking about minimum - sizes. + (Resizing Windows): Mention dividers when talking about minimum sizes. 2014-03-05 Glenn Morris @@ -349,8 +355,7 @@ 2013-12-28 Chong Yidong - * modes.texi (Auto Major Mode): Document interpreter-mode-alist - change. + * modes.texi (Auto Major Mode): Document interpreter-mode-alist change. * buffers.texi (Modification Time): Document visited-file-modtime change. @@ -387,8 +392,7 @@ * display.texi (Font Selection): Tweak example. - * commands.texi (Event Input Misc): Document new arg to - input-pending-p. + * commands.texi (Event Input Misc): Document new arg to input-pending-p. * nonascii.texi (Specifying Coding Systems): Don't refer to emacs-mule-dos. @@ -633,7 +637,8 @@ * display.texi (Showing Images): Add an index for image-size. Use @code instead of @var for a normal variable. (Multi-Frame Images): Improve indexing. - (Button Buffer Commands): Use @code instead of @var for a normal variable. + (Button Buffer Commands): Use @code instead of @var for a normal + variable. (Abstract Display): Explain the meaning of Ewoc. 2013-10-27 Xue Fuqiao diff --git a/doc/lispref/functions.texi b/doc/lispref/functions.texi index b85ed6e715c..faae0010f6e 100644 --- a/doc/lispref/functions.texi +++ b/doc/lispref/functions.texi @@ -11,23 +11,23 @@ explains what functions are, how they accept arguments, and how to define them. @menu -* What Is a Function:: Lisp functions vs. primitives; terminology. -* Lambda Expressions:: How functions are expressed as Lisp objects. -* Function Names:: A symbol can serve as the name of a function. -* Defining Functions:: Lisp expressions for defining functions. -* Calling Functions:: How to use an existing function. -* Mapping Functions:: Applying a function to each element of a list, etc. -* Anonymous Functions:: Lambda expressions are functions with no names. -* Function Cells:: Accessing or setting the function definition +* What Is a Function:: Lisp functions vs. primitives; terminology. +* Lambda Expressions:: How functions are expressed as Lisp objects. +* Function Names:: A symbol can serve as the name of a function. +* Defining Functions:: Lisp expressions for defining functions. +* Calling Functions:: How to use an existing function. +* Mapping Functions:: Applying a function to each element of a list, etc. +* Anonymous Functions:: Lambda expressions are functions with no names. +* Function Cells:: Accessing or setting the function definition of a symbol. -* Closures:: Functions that enclose a lexical environment. -* Advising Functions:: Adding to the definition of a function. -* Obsolete Functions:: Declaring functions obsolete. -* Inline Functions:: Functions that the compiler will expand inline. -* Declare Form:: Adding additional information about a function. -* Declaring Functions:: Telling the compiler that a function is defined. -* Function Safety:: Determining whether a function is safe to call. -* Related Topics:: Cross-references to specific Lisp primitives +* Closures:: Functions that enclose a lexical environment. +* Advising Functions:: Adding to the definition of a function. +* Obsolete Functions:: Declaring functions obsolete. +* Inline Functions:: Functions that the compiler will expand inline. +* Declare Form:: Adding additional information about a function. +* Declaring Functions:: Telling the compiler that a function is defined. +* Function Safety:: Determining whether a function is safe to call. +* Related Topics:: Cross-references to specific Lisp primitives that have a special bearing on how functions work. @end menu @@ -208,10 +208,10 @@ Before going into these details, the following subsections describe the components of a lambda expression and what they do. @menu -* Lambda Components:: The parts of a lambda expression. -* Simple Lambda:: A simple example. -* Argument List:: Details and special features of argument lists. -* Function Documentation:: How to put documentation in a function. +* Lambda Components:: The parts of a lambda expression. +* Simple Lambda:: A simple example. +* Argument List:: Details and special features of argument lists. +* Function Documentation:: How to put documentation in a function. @end menu @node Lambda Components @@ -1142,19 +1142,32 @@ examining or altering the structure of closure objects. @cindex advising functions @cindex piece of advice -Any variable or object field which holds a function can be modified with the -appropriate setter function, such as @code{set-process-filter}, @code{fset}, or -@code{setq}, but those can be too blunt, completely throwing away the +When you need to modify a function defined in another library, or when you need +to modify a hook like @code{@var{foo}-function}, a process filter, or basically +any variable or object field which holds a function value, you can use the +appropriate setter function, such as @code{fset} or @code{defun} for named +functions, @code{setq} for hook variables, or @code{set-process-filter} for +process filters, but those are often too blunt, completely throwing away the previous value. -In order to modify such hooks in a more controlled way, Emacs provides the -macros @code{add-function} and @code{remove-function}, which let you modify the -existing function value by composing it with another function. + The @dfn{advice} feature lets you add to the existing definition of +a function, by @dfn{advising the function}. This is a cleaner method +than redefining the whole function. -For example, in order to trace the calls to a process filter, you can use: +Emacs's advice system provides two sets of primitives for that: the core set, +for function values held in variables and object fields (with the corresponding +primitives being @code{add-function} and @code{remove-function}) and another +set layered on top of it for named functions (with the main primitives being +@code{advice-add} and @code{advice-remove}). + +For example, in order to trace the calls to the process filter of a process +@var{proc}, you could use: @example -(add-function :before (process-filter proc) #'my-tracing-function) +(defun my-tracing-function (proc string) + (message "Proc %S received %S" proc string)) + +(add-function :before (process-filter @var{proc}) #'my-tracing-function) @end example This will cause the process's output to be passed first to @@ -1162,33 +1175,55 @@ This will cause the process's output to be passed first to When you're done with it, you can revert to the untraced behavior with: @example -(remove-function (process-filter proc) #'my-tracing-function) +(remove-function (process-filter @var{proc}) #'my-tracing-function) @end example -The argument @code{:before} specifies how the two functions are composed, since -there are many different ways to do it. The added function is also called an -@emph{advice}. +Similarly, if you want to trace the execution of the function named +@code{display-buffer}, you could use: + +@example +(defun his-tracing-function (orig-fun &rest args) + (message "display-buffer called with args %S" args) + (let ((res (apply orig-fun args))) + (message "display-buffer returned %S" res) + res)) + +(advice-add 'display-buffer :around #'his-tracing-function) +@end example -The function cell of a symbol can be manipulated similarly, but since it can -contain other things than a plain function, you have to use @code{advice-add} -and @code{advice-remove} instead, which -@c use @code{add-function} and @code{remove-function} internally, but -know how to handle cases such as when the function cell holds a macro rather -than function, or when the function is autoloaded so the advice's activation -needs to be postponed. +and when you're tired of seeing this output, you can revert to the untraced +behavior with: + +@example +(advice-remove 'display-buffer #'his-tracing-function) +@end example + +The arguments @code{:before} and @code{:above} used in the above examples +specify how the two functions are composed, since there are many different +ways to do it. The added function is also called an @emph{advice}. @menu -* Advising Primitives:: Primitives to Manipulate Advices -* Advising Named Functions:: Advising Named Functions +* Core Advising Primitives:: Primitives to Manipulate Advices +* Advising Named Functions:: Advising Named Functions +* Porting old advices:: Adapting code using the old defadvice @end menu -@node Advising Primitives -@subsection Primitives to manipulate advice +@node Core Advising Primitives +@subsection Primitives to manipulate advices @defmac add-function where place function &optional props This macro is the handy way to add the advice @var{function} to the function stored in @var{place} (@pxref{Generalized Variables}). +If @var{function} is not interactive, then the combined function will inherit +the interactive spec, if any, of the original function. Else, the combined +function will be interactive and will use the interactive spec of +@var{function}. One exception: if the interactive spec of @var{function} +is a function (rather than an expression or a string), then the interactive +spec of the combined function will be a call to that function with as sole +argument the interactive spec of the original function. To interpret the spec +received as argument, use @code{advice-eval-interactive-spec}. + @var{where} determines how @var{function} is composed with the existing function. It can be one of the following: @@ -1340,21 +1375,39 @@ Call the function @var{f} for every advice that was added to and its properties. @end defun +@defun advice-eval-interactive-spec spec +Evaluate the interactive @var{spec} just like an interactive call to a function +with such a spec would, and then return the corresponding list of arguments +that was built. E.g. @code{(advice-eval-interactive-spec "r\nP")} will +return a list of three elements, containing the boundaries of the region and +the current prefix argument. +@end defun + @node Advising Named Functions @subsection Advising Named Functions A common use of advice is for named functions and macros. -Since @code{add-function} does not know how to deal with macros and -autoloaded functions, Emacs provides a separate set of functions to -manipulate pieces of advice applied to named functions. - - Advice can be useful for altering the behavior of an existing -function without having to redefine the whole function. However, it -can be a source of bugs, since existing callers to the function may -assume the old behavior, and work incorrectly when the behavior is -changed by advice. Advice can also cause confusion in debugging, if -the person doing the debugging does not notice or remember that the -function has been modified by advice. +You could just use @code{add-function} as in: + +@example +(add-function :around (symbol-function '@var{fun}) #'his-tracing-function) +@end example + + But you should use @code{advice-add} and @code{advice-remove} for that +instead. This separate set of functions to manipulate pieces of advice applied +to named functions, offers the following extra features compared to +@code{add-function}: they know how to deal with macros and autoloaded +functions, they let @code{describe-function} preserve the original docstring as +well as document the added advice, and they let you add and remove advices +before a function is even defined. + + @code{advice-add} can be useful for altering the behavior of existing calls +to an existing function without having to redefine the whole function. +However, it can be a source of bugs, since existing callers to the function may +assume the old behavior, and work incorrectly when the behavior is changed by +advice. Advice can also cause confusion in debugging, if the person doing the +debugging does not notice or remember that the function has been modified +by advice. For these reasons, advice should be reserved for the cases where you cannot modify a function's behavior in any other way. If it is @@ -1400,6 +1453,88 @@ Call @var{function} for every advice that was added to the named function and its properties. @end defun +@node Porting old advices +@subsection Adapting code using the old defadvice + +A lot of code uses the old @code{defadvice} mechanism, which is largely made +obsolete by the new @code{advice-add}, whose implementation and semantics is +significantly simpler. + +An old advice such as: + +@example +(defadvice previous-line (before next-line-at-end + (&optional arg try-vscroll)) + "Insert an empty line when moving up from the top line." + (if (and next-line-add-newlines (= arg 1) + (save-excursion (beginning-of-line) (bobp))) + (progn + (beginning-of-line) + (newline)))) +@end example + +could be translated in the new advice mechanism into a plain function: + +@example +(defun previous-line--next-line-at-end (&optional arg try-vscroll) + "Insert an empty line when moving up from the top line." + (if (and next-line-add-newlines (= arg 1) + (save-excursion (beginning-of-line) (bobp))) + (progn + (beginning-of-line) + (newline)))) +@end example + +Obviously, this does not actually modify @code{previous-line}. For that the +old advice needed: +@example +(ad-activate 'previous-line) +@end example +whereas the new advice mechanism needs: +@example +(advice-add 'previous-line :before #'previous-line--next-line-at-end) +@end example + +Note that @code{ad-activate} had a global effect: it activated all pieces of +advice enabled for that specified function. If you wanted to only activate or +deactivate a particular advice, you needed to @emph{enable} or @emph{disable} +that advice with @code{ad-enable-advice} and @code{ad-disable-advice}. +The new mechanism does away with this distinction. + +An around advice such as: + +@example +(defadvice foo (around foo-around) + "Ignore case in `foo'." + (let ((case-fold-search t)) + ad-do-it)) +(ad-activate 'foo) +@end example + +could translate into: + +@example +(defun foo--foo-around (orig-fun &rest args) + "Ignore case in `foo'." + (let ((case-fold-search t)) + (apply orig-fun args))) +(advice-add 'foo :around #'foo--foo-around) +@end example + +Regarding the advice's @emph{class}, note that the new @code{:before} is not +quite equivalent to the old @code{before}, because in the old advice you could +modify the function's arguments (e.g., with @code{ad-set-arg}), and that would +affect the argument values seen by the original function, whereas in the new +@code{:before}, modifying an argument via @code{setq} in the advice has no +effect on the arguments seen by the original function. +When porting a @code{before} advice which relied on this behavior, you'll need +to turn it into a new @code{:around} or @code{:filter-args} advice instead. + +Similarly an old @code{after} advice could modify the returned value by +changing @code{ad-return-value}, whereas a new @code{:after} advice cannot, so +when porting such an old @code{after} advice, you'll need to turn it into a new +@code{:around} or @code{:filter-return} advice instead. + @node Obsolete Functions @section Declaring Functions Obsolete @cindex obsolete functions diff --git a/lisp/ChangeLog b/lisp/ChangeLog index 69419a3d1ea..3cec8c34a2c 100644 --- a/lisp/ChangeLog +++ b/lisp/ChangeLog @@ -27,8 +27,8 @@ * newcomment.el (comment-beginning): If `comment-start-skip' doesn't match, move back one char and try again. (Bug#16971) - * emacs-lisp/lisp-mode.el (lisp-mode-variables): Set - `comment-use-syntax' to t to avoid the unnecessary runtime check. + * emacs-lisp/lisp-mode.el (lisp-mode-variables): + Set `comment-use-syntax' to t to avoid the unnecessary runtime check. Set `comment-start-skip' to a simpler value that doesn't try to check if the semicolon is escaped (this is handled by `syntax-ppss' now). (Bug#16971)