[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Emacs-diffs] Changes to compile.texi
|
From: |
Glenn Morris |
|
Subject: |
[Emacs-diffs] Changes to compile.texi |
|
Date: |
Thu, 06 Sep 2007 04:18:34 +0000 |
CVSROOT: /sources/emacs
Module name: emacs
Changes by: Glenn Morris <gm> 07/09/06 04:18:34
Index: compile.texi
===================================================================
RCS file: compile.texi
diff -N compile.texi
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ compile.texi 6 Sep 2007 04:18:34 -0000 1.1
@@ -0,0 +1,886 @@
address@hidden -*-texinfo-*-
address@hidden This is part of the GNU Emacs Lisp Reference Manual.
address@hidden Copyright (C) 1990, 1991, 1992, 1993, 1994, 2001, 2002, 2003,
2004,
address@hidden 2005, 2006, 2007 Free Software Foundation, Inc.
address@hidden See the file elisp.texi for copying conditions.
address@hidden ../info/compile
address@hidden Byte Compilation, Advising Functions, Loading, Top
address@hidden Byte Compilation
address@hidden byte compilation
address@hidden byte-code
address@hidden compilation (Emacs Lisp)
+
+ Emacs Lisp has a @dfn{compiler} that translates functions written
+in Lisp into a special representation called @dfn{byte-code} that can be
+executed more efficiently. The compiler replaces Lisp function
+definitions with byte-code. When a byte-code function is called, its
+definition is evaluated by the @dfn{byte-code interpreter}.
+
+ Because the byte-compiled code is evaluated by the byte-code
+interpreter, instead of being executed directly by the machine's
+hardware (as true compiled code is), byte-code is completely
+transportable from machine to machine without recompilation. It is not,
+however, as fast as true compiled code.
+
+ Compiling a Lisp file with the Emacs byte compiler always reads the
+file as multibyte text, even if Emacs was started with @samp{--unibyte},
+unless the file specifies otherwise. This is so that compilation gives
+results compatible with running the same file without compilation.
address@hidden Non-ASCII}.
+
+ In general, any version of Emacs can run byte-compiled code produced
+by recent earlier versions of Emacs, but the reverse is not true.
+
address@hidden no-byte-compile
+ If you do not want a Lisp file to be compiled, ever, put a file-local
+variable binding for @code{no-byte-compile} into it, like this:
+
address@hidden
+;; -*-no-byte-compile: t; -*-
address@hidden example
+
+ @xref{Compilation Errors}, for how to investigate errors occurring in
+byte compilation.
+
address@hidden
+* Speed of Byte-Code:: An example of speedup from byte compilation.
+* Compilation Functions:: Byte compilation functions.
+* Docs and Compilation:: Dynamic loading of documentation strings.
+* Dynamic Loading:: Dynamic loading of individual functions.
+* Eval During Compile:: Code to be evaluated when you compile.
+* Compiler Errors:: Handling compiler error messages.
+* Byte-Code Objects:: The data type used for byte-compiled functions.
+* Disassembly:: Disassembling byte-code; how to read byte-code.
address@hidden menu
+
address@hidden Speed of Byte-Code
address@hidden Performance of Byte-Compiled Code
+
+ A byte-compiled function is not as efficient as a primitive function
+written in C, but runs much faster than the version written in Lisp.
+Here is an example:
+
address@hidden
address@hidden
+(defun silly-loop (n)
+ "Return time before and after N iterations of a loop."
+ (let ((t1 (current-time-string)))
+ (while (> (setq n (1- n))
+ 0))
+ (list t1 (current-time-string))))
address@hidden silly-loop
address@hidden group
+
address@hidden
+(silly-loop 100000)
address@hidden ("Fri Mar 18 17:25:57 1994"
+ "Fri Mar 18 17:26:28 1994") ; @r{31 seconds}
address@hidden group
+
address@hidden
+(byte-compile 'silly-loop)
address@hidden @r{[Compiled code not shown]}
address@hidden group
+
address@hidden
+(silly-loop 100000)
address@hidden ("Fri Mar 18 17:26:52 1994"
+ "Fri Mar 18 17:26:58 1994") ; @r{6 seconds}
address@hidden group
address@hidden example
+
+ In this example, the interpreted code required 31 seconds to run,
+whereas the byte-compiled code required 6 seconds. These results are
+representative, but actual results will vary greatly.
+
address@hidden Compilation Functions
address@hidden node-name, next, previous, up
address@hidden The Compilation Functions
address@hidden compilation functions
+
+ You can byte-compile an individual function or macro definition with
+the @code{byte-compile} function. You can compile a whole file with
address@hidden, or several files with
address@hidden or @code{batch-byte-compile}.
+
+ The byte compiler produces error messages and warnings about each file
+in a buffer called @samp{*Compile-Log*}. These report things in your
+program that suggest a problem but are not necessarily erroneous.
+
address@hidden macro compilation
+ Be careful when writing macro calls in files that you may someday
+byte-compile. Macro calls are expanded when they are compiled, so the
+macros must already be defined for proper compilation. For more
+details, see @ref{Compiling Macros}. If a program does not work the
+same way when compiled as it does when interpreted, erroneous macro
+definitions are one likely cause (@pxref{Problems with Macros}).
+Inline (@code{defsubst}) functions are less troublesome; if you
+compile a call to such a function before its definition is known, the
+call will still work right, it will just run slower.
+
+ Normally, compiling a file does not evaluate the file's contents or
+load the file. But it does execute any @code{require} calls at top
+level in the file. One way to ensure that necessary macro definitions
+are available during compilation is to require the file that defines
+them (@pxref{Named Features}). To avoid loading the macro definition files
+when someone @emph{runs} the compiled program, write
address@hidden around the @code{require} calls (@pxref{Eval
+During Compile}).
+
address@hidden byte-compile symbol
+This function byte-compiles the function definition of @var{symbol},
+replacing the previous definition with the compiled one. The function
+definition of @var{symbol} must be the actual code for the function;
+i.e., the compiler does not follow indirection to another symbol.
address@hidden returns the new, compiled definition of
address@hidden
+
+ If @var{symbol}'s definition is a byte-code function object,
address@hidden does nothing and returns @code{nil}. Lisp records
+only one function definition for any symbol, and if that is already
+compiled, non-compiled code is not available anywhere. So there is no
+way to ``compile the same definition again.''
+
address@hidden
address@hidden
+(defun factorial (integer)
+ "Compute factorial of INTEGER."
+ (if (= 1 integer) 1
+ (* integer (factorial (1- integer)))))
address@hidden factorial
address@hidden group
+
address@hidden
+(byte-compile 'factorial)
address@hidden
+#[(integer)
+ "^H\301U\203^H^@@\301\207\302^H\303^HS!\"\207"
+ [integer 1 * factorial]
+ 4 "Compute factorial of INTEGER."]
address@hidden group
address@hidden example
+
address@hidden
+The result is a byte-code function object. The string it contains is
+the actual byte-code; each character in it is an instruction or an
+operand of an instruction. The vector contains all the constants,
+variable names and function names used by the function, except for
+certain primitives that are coded as special instructions.
+
+If the argument to @code{byte-compile} is a @code{lambda} expression,
+it returns the corresponding compiled code, but does not store
+it anywhere.
address@hidden defun
+
address@hidden Command compile-defun &optional arg
+This command reads the defun containing point, compiles it, and
+evaluates the result. If you use this on a defun that is actually a
+function definition, the effect is to install a compiled version of that
+function.
+
address@hidden normally displays the result of evaluation in the
+echo area, but if @var{arg} is address@hidden, it inserts the result
+in the current buffer after the form it compiled.
address@hidden deffn
+
address@hidden Command byte-compile-file filename &optional load
+This function compiles a file of Lisp code named @var{filename} into a
+file of byte-code. The output file's name is made by changing the
address@hidden suffix into @samp{.elc}; if @var{filename} does not end in
address@hidden, it adds @samp{.elc} to the end of @var{filename}.
+
+Compilation works by reading the input file one form at a time. If it
+is a definition of a function or macro, the compiled function or macro
+definition is written out. Other forms are batched together, then each
+batch is compiled, and written so that its compiled code will be
+executed when the file is read. All comments are discarded when the
+input file is read.
+
+This command returns @code{t} if there were no errors and @code{nil}
+otherwise. When called interactively, it prompts for the file name.
+
+If @var{load} is address@hidden, this command loads the compiled file
+after compiling it. Interactively, @var{load} is the prefix argument.
+
address@hidden
address@hidden
+% ls -l push*
+-rw-r--r-- 1 lewis 791 Oct 5 20:31 push.el
address@hidden group
+
address@hidden
+(byte-compile-file "~/emacs/push.el")
+ @result{} t
address@hidden group
+
address@hidden
+% ls -l push*
+-rw-r--r-- 1 lewis 791 Oct 5 20:31 push.el
+-rw-rw-rw- 1 lewis 638 Oct 8 20:25 push.elc
address@hidden group
address@hidden example
address@hidden deffn
+
address@hidden Command byte-recompile-directory directory &optional flag force
address@hidden library compilation
+This command recompiles every @samp{.el} file in @var{directory} (or
+its subdirectories) that needs recompilation. A file needs
+recompilation if a @samp{.elc} file exists but is older than the
address@hidden file.
+
+When a @samp{.el} file has no corresponding @samp{.elc} file,
address@hidden says what to do. If it is @code{nil}, this command ignores
+these files. If @var{flag} is 0, it compiles them. If it is neither
address@hidden nor 0, it asks the user whether to compile each such file,
+and asks about each subdirectory as well.
+
+Interactively, @code{byte-recompile-directory} prompts for
address@hidden and @var{flag} is the prefix argument.
+
+If @var{force} is address@hidden, this command recompiles every
address@hidden file that has a @samp{.elc} file.
+
+The returned value is unpredictable.
address@hidden deffn
+
address@hidden batch-byte-compile &optional noforce
+This function runs @code{byte-compile-file} on files specified on the
+command line. This function must be used only in a batch execution of
+Emacs, as it kills Emacs on completion. An error in one file does not
+prevent processing of subsequent files, but no output file will be
+generated for it, and the Emacs process will terminate with a nonzero
+status code.
+
+If @var{noforce} is address@hidden, this function does not recompile
+files that have an up-to-date @samp{.elc} file.
+
address@hidden
+% emacs -batch -f batch-byte-compile *.el
address@hidden example
address@hidden defun
+
address@hidden byte-code code-string data-vector max-stack
address@hidden byte-code interpreter
+This function actually interprets byte-code. A byte-compiled function
+is actually defined with a body that calls @code{byte-code}. Don't call
+this function yourself---only the byte compiler knows how to generate
+valid calls to this function.
+
+In Emacs version 18, byte-code was always executed by way of a call to
+the function @code{byte-code}. Nowadays, byte-code is usually executed
+as part of a byte-code function object, and only rarely through an
+explicit call to @code{byte-code}.
address@hidden defun
+
address@hidden Docs and Compilation
address@hidden Documentation Strings and Compilation
address@hidden dynamic loading of documentation
+
+ Functions and variables loaded from a byte-compiled file access their
+documentation strings dynamically from the file whenever needed. This
+saves space within Emacs, and makes loading faster because the
+documentation strings themselves need not be processed while loading the
+file. Actual access to the documentation strings becomes slower as a
+result, but this normally is not enough to bother users.
+
+ Dynamic access to documentation strings does have drawbacks:
+
address@hidden @bullet
address@hidden
+If you delete or move the compiled file after loading it, Emacs can no
+longer access the documentation strings for the functions and variables
+in the file.
+
address@hidden
+If you alter the compiled file (such as by compiling a new version),
+then further access to documentation strings in this file will
+probably give nonsense results.
address@hidden itemize
+
+ If your site installs Emacs following the usual procedures, these
+problems will never normally occur. Installing a new version uses a new
+directory with a different name; as long as the old version remains
+installed, its files will remain unmodified in the places where they are
+expected to be.
+
+ However, if you have built Emacs yourself and use it from the
+directory where you built it, you will experience this problem
+occasionally if you edit and recompile Lisp files. When it happens, you
+can cure the problem by reloading the file after recompiling it.
+
+ You can turn off this feature at compile time by setting
address@hidden to @code{nil}; this is useful
+mainly if you expect to change the file, and you want Emacs processes
+that have already loaded it to keep working when the file changes.
+You can do this globally, or for one source file by specifying a
+file-local binding for the variable. One way to do that is by adding
+this string to the file's first line:
+
address@hidden
+-*-byte-compile-dynamic-docstrings: nil;-*-
address@hidden example
+
address@hidden byte-compile-dynamic-docstrings
+If this is address@hidden, the byte compiler generates compiled files
+that are set up for dynamic loading of documentation strings.
address@hidden defvar
+
address@hidden @samp{#@@@var{count}}
address@hidden @samp{#$}
+ The dynamic documentation string feature writes compiled files that
+use a special Lisp reader construct, @samp{#@@@var{count}}. This
+construct skips the next @var{count} characters. It also uses the
address@hidden construct, which stands for ``the name of this file, as a
+string.'' It is usually best not to use these constructs in Lisp source
+files, since they are not designed to be clear to humans reading the
+file.
+
address@hidden Dynamic Loading
address@hidden Dynamic Loading of Individual Functions
+
address@hidden dynamic loading of functions
address@hidden lazy loading
+ When you compile a file, you can optionally enable the @dfn{dynamic
+function loading} feature (also known as @dfn{lazy loading}). With
+dynamic function loading, loading the file doesn't fully read the
+function definitions in the file. Instead, each function definition
+contains a place-holder which refers to the file. The first time each
+function is called, it reads the full definition from the file, to
+replace the place-holder.
+
+ The advantage of dynamic function loading is that loading the file
+becomes much faster. This is a good thing for a file which contains
+many separate user-callable functions, if using one of them does not
+imply you will probably also use the rest. A specialized mode which
+provides many keyboard commands often has that usage pattern: a user may
+invoke the mode, but use only a few of the commands it provides.
+
+ The dynamic loading feature has certain disadvantages:
+
address@hidden @bullet
address@hidden
+If you delete or move the compiled file after loading it, Emacs can no
+longer load the remaining function definitions not already loaded.
+
address@hidden
+If you alter the compiled file (such as by compiling a new version),
+then trying to load any function not already loaded will usually yield
+nonsense results.
address@hidden itemize
+
+ These problems will never happen in normal circumstances with
+installed Emacs files. But they are quite likely to happen with Lisp
+files that you are changing. The easiest way to prevent these problems
+is to reload the new compiled file immediately after each recompilation.
+
+ The byte compiler uses the dynamic function loading feature if the
+variable @code{byte-compile-dynamic} is address@hidden at compilation
+time. Do not set this variable globally, since dynamic loading is
+desirable only for certain files. Instead, enable the feature for
+specific source files with file-local variable bindings. For example,
+you could do it by writing this text in the source file's first line:
+
address@hidden
+-*-byte-compile-dynamic: t;-*-
address@hidden example
+
address@hidden byte-compile-dynamic
+If this is address@hidden, the byte compiler generates compiled files
+that are set up for dynamic function loading.
address@hidden defvar
+
address@hidden fetch-bytecode function
+If @var{function} is a byte-code function object, this immediately
+finishes loading the byte code of @var{function} from its
+byte-compiled file, if it is not fully loaded already. Otherwise,
+it does nothing. It always returns @var{function}.
address@hidden defun
+
address@hidden Eval During Compile
address@hidden Evaluation During Compilation
+
+ These features permit you to write code to be evaluated during
+compilation of a program.
+
address@hidden eval-and-compile address@hidden
+This form marks @var{body} to be evaluated both when you compile the
+containing code and when you run it (whether compiled or not).
+
+You can get a similar result by putting @var{body} in a separate file
+and referring to that file with @code{require}. That method is
+preferable when @var{body} is large. Effectively @code{require} is
+automatically @code{eval-and-compile}, the package is loaded both when
+compiling and executing.
+
address@hidden is also effectively @code{eval-and-compile} too. It's
+recognized when compiling, so uses of such a function don't produce
+``not known to be defined'' warnings.
+
+Most uses of @code{eval-and-compile} are fairly sophisticated.
+
+If a macro has a helper function to build its result, and that macro
+is used both locally and outside the package, then
address@hidden should be used to get the helper both when
+compiling and then later when running.
+
+If functions are defined programmatically (with @code{fset} say), then
address@hidden can be used to have that done at compile-time
+as well as run-time, so calls to those functions are checked (and
+warnings about ``not known to be defined'' suppressed).
address@hidden defspec
+
address@hidden eval-when-compile address@hidden
+This form marks @var{body} to be evaluated at compile time but not when
+the compiled program is loaded. The result of evaluation by the
+compiler becomes a constant which appears in the compiled program. If
+you load the source file, rather than compiling it, @var{body} is
+evaluated normally.
+
address@hidden compile-time constant
+If you have a constant that needs some calculation to produce,
address@hidden can do that at compile-time. For example,
+
address@hidden
+(defvar my-regexp
+ (eval-when-compile (regexp-opt '("aaa" "aba" "abb"))))
address@hidden lisp
+
address@hidden macros, at compile time
+If you're using another package, but only need macros from it (the
+byte compiler will expand those), then @code{eval-when-compile} can be
+used to load it for compiling, but not executing. For example,
+
address@hidden
+(eval-when-compile
+ (require 'my-macro-package)) ;; only macros needed from this
address@hidden lisp
+
+The same sort of thing goes for macros and @code{defsubst} functions
+defined locally and only for use within the file. They are needed for
+compiling the file, but in most cases they are not needed for
+execution of the compiled file. For example,
+
address@hidden
+(eval-when-compile
+ (unless (fboundp 'some-new-thing)
+ (defmacro 'some-new-thing ()
+ (compatibility code))))
address@hidden lisp
+
address@hidden
+This is often good for code that's only a fallback for compatibility
+with other versions of Emacs.
+
address@hidden Lisp Note:} At top level, @code{eval-when-compile} is analogous
to the Common
+Lisp idiom @code{(eval-when (compile eval) @dots{})}. Elsewhere, the
+Common Lisp @samp{#.} reader macro (but not when interpreting) is closer
+to what @code{eval-when-compile} does.
address@hidden defspec
+
address@hidden Compiler Errors
address@hidden Compiler Errors
address@hidden compiler errors
+
+ Byte compilation outputs all errors and warnings into the buffer
address@hidden The messages include file names and line
+numbers that identify the location of the problem. The usual Emacs
+commands for operating on compiler diagnostics work properly on
+these messages.
+
+ However, the warnings about functions that were used but not
+defined are always ``located'' at the end of the file, so these
+commands won't find the places they are really used. To do that,
+you must search for the function names.
+
+ You can suppress the compiler warning for calling an undefined
+function @var{func} by conditionalizing the function call on an
address@hidden test, like this:
+
address@hidden
+(if (fboundp '@var{func}) ...(@var{func} ...)...)
address@hidden example
+
address@hidden
+The call to @var{func} must be in the @var{then-form} of the
address@hidden, and @var{func} must appear quoted in the call to
address@hidden (This feature operates for @code{cond} as well.)
+
+ Likewise, you can suppress a compiler warning for an unbound variable
address@hidden by conditionalizing its use on a @code{boundp} test,
+like this:
+
address@hidden
+(if (boundp '@var{variable}) address@hidden)
address@hidden example
+
address@hidden
+The reference to @var{variable} must be in the @var{then-form} of the
address@hidden, and @var{variable} must appear quoted in the call to
address@hidden
+
+ You can suppress any compiler warnings using the construct
address@hidden:
+
address@hidden This is implemented with a defun, but conceptually it is
address@hidden a special form.
+
address@hidden with-no-warnings address@hidden
+In execution, this is equivalent to @code{(progn @var{body}...)},
+but the compiler does not issue warnings for anything that occurs
+inside @var{body}.
+
+We recommend that you use this construct around the smallest
+possible piece of code.
address@hidden defspec
+
address@hidden Byte-Code Objects
address@hidden Byte-Code Function Objects
address@hidden compiled function
address@hidden byte-code function
+
+ Byte-compiled functions have a special data type: they are
address@hidden function objects}.
+
+ Internally, a byte-code function object is much like a vector;
+however, the evaluator handles this data type specially when it appears
+as a function to be called. The printed representation for a byte-code
+function object is like that for a vector, with an additional @samp{#}
+before the opening @samp{[}.
+
+ A byte-code function object must have at least four elements; there is
+no maximum number, but only the first six elements have any normal use.
+They are:
+
address@hidden @var
address@hidden arglist
+The list of argument symbols.
+
address@hidden byte-code
+The string containing the byte-code instructions.
+
address@hidden constants
+The vector of Lisp objects referenced by the byte code. These include
+symbols used as function names and variable names.
+
address@hidden stacksize
+The maximum stack size this function needs.
+
address@hidden docstring
+The documentation string (if any); otherwise, @code{nil}. The value may
+be a number or a list, in case the documentation string is stored in a
+file. Use the function @code{documentation} to get the real
+documentation string (@pxref{Accessing Documentation}).
+
address@hidden interactive
+The interactive spec (if any). This can be a string or a Lisp
+expression. It is @code{nil} for a function that isn't interactive.
address@hidden table
+
+Here's an example of a byte-code function object, in printed
+representation. It is the definition of the command
address@hidden
+
address@hidden
+#[(&optional arg)
+ "^H\204^F^@@\301^P\302^H[!\207"
+ [arg 1 forward-sexp]
+ 2
+ 254435
+ "p"]
address@hidden example
+
+ The primitive way to create a byte-code object is with
address@hidden:
+
address@hidden make-byte-code &rest elements
+This function constructs and returns a byte-code function object
+with @var{elements} as its elements.
address@hidden defun
+
+ You should not try to come up with the elements for a byte-code
+function yourself, because if they are inconsistent, Emacs may crash
+when you call the function. Always leave it to the byte compiler to
+create these objects; it makes the elements consistent (we hope).
+
+ You can access the elements of a byte-code object using @code{aref};
+you can also use @code{vconcat} to create a vector with the same
+elements.
+
address@hidden Disassembly
address@hidden Disassembled Byte-Code
address@hidden disassembled byte-code
+
+ People do not write byte-code; that job is left to the byte compiler.
+But we provide a disassembler to satisfy a cat-like curiosity. The
+disassembler converts the byte-compiled code into humanly readable
+form.
+
+ The byte-code interpreter is implemented as a simple stack machine.
+It pushes values onto a stack of its own, then pops them off to use them
+in calculations whose results are themselves pushed back on the stack.
+When a byte-code function returns, it pops a value off the stack and
+returns it as the value of the function.
+
+ In addition to the stack, byte-code functions can use, bind, and set
+ordinary Lisp variables, by transferring values between variables and
+the stack.
+
address@hidden Command disassemble object &optional buffer-or-name
+This command displays the disassembled code for @var{object}. In
+interactive use, or if @var{buffer-or-name} is @code{nil} or omitted,
+the output goes in a buffer named @samp{*Disassemble*}. If
address@hidden is address@hidden, it must be a buffer or the
+name of an existing buffer. Then the output goes there, at point, and
+point is left before the output.
+
+The argument @var{object} can be a function name, a lambda expression
+or a byte-code object. If it is a lambda expression, @code{disassemble}
+compiles it and disassembles the resulting compiled code.
address@hidden deffn
+
+ Here are two examples of using the @code{disassemble} function. We
+have added explanatory comments to help you relate the byte-code to the
+Lisp source; these do not appear in the output of @code{disassemble}.
+These examples show unoptimized byte-code. Nowadays byte-code is
+usually optimized, but we did not want to rewrite these examples, since
+they still serve their purpose.
+
address@hidden
address@hidden
+(defun factorial (integer)
+ "Compute factorial of an integer."
+ (if (= 1 integer) 1
+ (* integer (factorial (1- integer)))))
+ @result{} factorial
address@hidden group
+
address@hidden
+(factorial 4)
+ @result{} 24
address@hidden group
+
address@hidden
+(disassemble 'factorial)
+ @print{} byte-code for factorial:
+ doc: Compute factorial of an integer.
+ args: (integer)
address@hidden group
+
address@hidden
+0 constant 1 ; @r{Push 1 onto stack.}
+
+1 varref integer ; @r{Get value of @code{integer}}
+ ; @r{from the environment}
+ ; @r{and push the value}
+ ; @r{onto the stack.}
address@hidden group
+
address@hidden
+2 eqlsign ; @r{Pop top two values off stack,}
+ ; @r{compare them,}
+ ; @r{and push result onto stack.}
address@hidden group
+
address@hidden
+3 goto-if-nil 10 ; @r{Pop and test top of stack;}
+ ; @r{if @code{nil}, go to 10,}
+ ; @r{else continue.}
address@hidden group
+
address@hidden
+6 constant 1 ; @r{Push 1 onto top of stack.}
+
+7 goto 17 ; @r{Go to 17 (in this case, 1 will be}
+ ; @r{returned by the function).}
address@hidden group
+
address@hidden
+10 constant * ; @r{Push symbol @code{*} onto stack.}
+
+11 varref integer ; @r{Push value of @code{integer} onto stack.}
address@hidden group
+
address@hidden
+12 constant factorial ; @r{Push @code{factorial} onto stack.}
+
+13 varref integer ; @r{Push value of @code{integer} onto stack.}
+
+14 sub1 ; @r{Pop @code{integer}, decrement value,}
+ ; @r{push new value onto stack.}
address@hidden group
+
address@hidden
+ ; @r{Stack now contains:}
+ ; @minus{} @r{decremented value of
@code{integer}}
+ ; @minus{} @address@hidden
+ ; @minus{} @r{value of @code{integer}}
+ ; @minus{} @address@hidden
address@hidden group
+
address@hidden
+15 call 1 ; @r{Call function @code{factorial} using}
+ ; @r{the first (i.e., the top) element}
+ ; @r{of the stack as the argument;}
+ ; @r{push returned value onto stack.}
address@hidden group
+
address@hidden
+ ; @r{Stack now contains:}
+ ; @minus{} @r{result of recursive}
+ ; @r{call to @code{factorial}}
+ ; @minus{} @r{value of @code{integer}}
+ ; @minus{} @address@hidden
address@hidden group
+
address@hidden
+16 call 2 ; @r{Using the first two}
+ ; @r{(i.e., the top two)}
+ ; @r{elements of the stack}
+ ; @r{as arguments,}
+ ; @r{call the function @code{*},}
+ ; @r{pushing the result onto the stack.}
address@hidden group
+
address@hidden
+17 return ; @r{Return the top element}
+ ; @r{of the stack.}
+ @result{} nil
address@hidden group
address@hidden example
+
+The @code{silly-loop} function is somewhat more complex:
+
address@hidden
address@hidden
+(defun silly-loop (n)
+ "Return time before and after N iterations of a loop."
+ (let ((t1 (current-time-string)))
+ (while (> (setq n (1- n))
+ 0))
+ (list t1 (current-time-string))))
+ @result{} silly-loop
address@hidden group
+
address@hidden
+(disassemble 'silly-loop)
+ @print{} byte-code for silly-loop:
+ doc: Return time before and after N iterations of a loop.
+ args: (n)
+
+0 constant current-time-string ; @r{Push}
+ ; @address@hidden
+ ; @r{onto top of stack.}
address@hidden group
+
address@hidden
+1 call 0 ; @r{Call @code{current-time-string}}
+ ; @r{ with no argument,}
+ ; @r{ pushing result onto stack.}
address@hidden group
+
address@hidden
+2 varbind t1 ; @r{Pop stack and bind @code{t1}}
+ ; @r{to popped value.}
address@hidden group
+
address@hidden
+3 varref n ; @r{Get value of @code{n} from}
+ ; @r{the environment and push}
+ ; @r{the value onto the stack.}
address@hidden group
+
address@hidden
+4 sub1 ; @r{Subtract 1 from top of stack.}
address@hidden group
+
address@hidden
+5 dup ; @r{Duplicate the top of the stack;}
+ ; @r{i.e., copy the top of}
+ ; @r{the stack and push the}
+ ; @r{copy onto the stack.}
address@hidden group
+
address@hidden
+6 varset n ; @r{Pop the top of the stack,}
+ ; @r{and bind @code{n} to the value.}
+
+ ; @r{In effect, the sequence @code{dup varset}}
+ ; @r{copies the top of the stack}
+ ; @r{into the value of @code{n}}
+ ; @r{without popping it.}
address@hidden group
+
address@hidden
+7 constant 0 ; @r{Push 0 onto stack.}
address@hidden group
+
address@hidden
+8 gtr ; @r{Pop top two values off stack,}
+ ; @r{test if @var{n} is greater than 0}
+ ; @r{and push result onto stack.}
address@hidden group
+
address@hidden
+9 goto-if-nil-else-pop 17 ; @r{Goto 17 if @code{n} <= 0}
+ ; @r{(this exits the while loop).}
+ ; @r{else pop top of stack}
+ ; @r{and continue}
address@hidden group
+
address@hidden
+12 constant nil ; @r{Push @code{nil} onto stack}
+ ; @r{(this is the body of the loop).}
address@hidden group
+
address@hidden
+13 discard ; @r{Discard result of the body}
+ ; @r{of the loop (a while loop}
+ ; @r{is always evaluated for}
+ ; @r{its side effects).}
address@hidden group
+
address@hidden
+14 goto 3 ; @r{Jump back to beginning}
+ ; @r{of while loop.}
address@hidden group
+
address@hidden
+17 discard ; @r{Discard result of while loop}
+ ; @r{by popping top of stack.}
+ ; @r{This result is the value @code{nil} that}
+ ; @r{was not popped by the goto at 9.}
address@hidden group
+
address@hidden
+18 varref t1 ; @r{Push value of @code{t1} onto stack.}
address@hidden group
+
address@hidden
+19 constant current-time-string ; @r{Push}
+ ; @address@hidden
+ ; @r{onto top of stack.}
address@hidden group
+
address@hidden
+20 call 0 ; @r{Call @code{current-time-string} again.}
address@hidden group
+
address@hidden
+21 list2 ; @r{Pop top two elements off stack,}
+ ; @r{create a list of them,}
+ ; @r{and push list onto stack.}
address@hidden group
+
address@hidden
+22 unbind 1 ; @r{Unbind @code{t1} in local environment.}
+
+23 return ; @r{Return value of the top of stack.}
+
+ @result{} nil
address@hidden group
address@hidden example
+
+
address@hidden
+ arch-tag: f78e3050-2f0a-4dee-be27-d9979a0a2289
address@hidden ignore