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diff --git a/lispref/compile.texi b/lispref/compile.texi deleted file mode 100644 index f3a26d77322..00000000000 --- a/lispref/compile.texi +++ /dev/null @@ -1,886 +0,0 @@ -@c -*-texinfo-*- -@c This is part of the GNU Emacs Lisp Reference Manual. -@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 2001, 2002, 2003, 2004, -@c 2005, 2006, 2007, 2008 Free Software Foundation, Inc. -@c See the file elisp.texi for copying conditions. -@setfilename ../info/compile -@node Byte Compilation, Advising Functions, Loading, Top -@chapter Byte Compilation -@cindex byte compilation -@cindex byte-code -@cindex 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. -@xref{Loading 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. - -@vindex 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: - -@example -;; -*-no-byte-compile: t; -*- -@end example - - @xref{Compilation Errors}, for how to investigate errors occurring in -byte compilation. - -@menu -* 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. -@end menu - -@node Speed of Byte-Code -@section 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: - -@example -@group -(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 -@end group - -@group -(silly-loop 100000) -@result{} ("Fri Mar 18 17:25:57 1994" - "Fri Mar 18 17:26:28 1994") ; @r{31 seconds} -@end group - -@group -(byte-compile 'silly-loop) -@result{} @r{[Compiled code not shown]} -@end group - -@group -(silly-loop 100000) -@result{} ("Fri Mar 18 17:26:52 1994" - "Fri Mar 18 17:26:58 1994") ; @r{6 seconds} -@end group -@end 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. - -@node Compilation Functions -@comment node-name, next, previous, up -@section The Compilation Functions -@cindex 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 -@code{byte-compile-file}, or several files with -@code{byte-recompile-directory} 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. - -@cindex 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 -@code{eval-when-compile} around the @code{require} calls (@pxref{Eval -During Compile}). - -@defun 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. -@code{byte-compile} returns the new, compiled definition of -@var{symbol}. - - If @var{symbol}'s definition is a byte-code function object, -@code{byte-compile} 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.'' - -@example -@group -(defun factorial (integer) - "Compute factorial of INTEGER." - (if (= 1 integer) 1 - (* integer (factorial (1- integer))))) -@result{} factorial -@end group - -@group -(byte-compile 'factorial) -@result{} -#[(integer) - "^H\301U\203^H^@@\301\207\302^H\303^HS!\"\207" - [integer 1 * factorial] - 4 "Compute factorial of INTEGER."] -@end group -@end example - -@noindent -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. -@end defun - -@deffn 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. - -@code{compile-defun} normally displays the result of evaluation in the -echo area, but if @var{arg} is non-@code{nil}, it inserts the result -in the current buffer after the form it compiled. -@end deffn - -@deffn 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 -@samp{.el} suffix into @samp{.elc}; if @var{filename} does not end in -@samp{.el}, 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 non-@code{nil}, this command loads the compiled file -after compiling it. Interactively, @var{load} is the prefix argument. - -@example -@group -% ls -l push* --rw-r--r-- 1 lewis 791 Oct 5 20:31 push.el -@end group - -@group -(byte-compile-file "~/emacs/push.el") - @result{} t -@end group - -@group -% 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 -@end group -@end example -@end deffn - -@deffn Command byte-recompile-directory directory &optional flag force -@cindex 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 -@samp{.el} file. - -When a @samp{.el} file has no corresponding @samp{.elc} file, -@var{flag} 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 -@code{nil} 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 -@var{directory} and @var{flag} is the prefix argument. - -If @var{force} is non-@code{nil}, this command recompiles every -@samp{.el} file that has a @samp{.elc} file. - -The returned value is unpredictable. -@end deffn - -@defun 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 non-@code{nil}, this function does not recompile -files that have an up-to-date @samp{.elc} file. - -@example -% emacs -batch -f batch-byte-compile *.el -@end example -@end defun - -@defun byte-code code-string data-vector max-stack -@cindex 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}. -@end defun - -@node Docs and Compilation -@section Documentation Strings and Compilation -@cindex 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: - -@itemize @bullet -@item -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. - -@item -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. -@end 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 -@code{byte-compile-dynamic-docstrings} 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: - -@example --*-byte-compile-dynamic-docstrings: nil;-*- -@end example - -@defvar byte-compile-dynamic-docstrings -If this is non-@code{nil}, the byte compiler generates compiled files -that are set up for dynamic loading of documentation strings. -@end defvar - -@cindex @samp{#@@@var{count}} -@cindex @samp{#$} - The dynamic documentation string feature writes compiled files that -use a special Lisp reader construct, @samp{#@@@var{count}}. This -construct skips the next @var{count} characters. It also uses the -@samp{#$} 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. - -@node Dynamic Loading -@section Dynamic Loading of Individual Functions - -@cindex dynamic loading of functions -@cindex 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: - -@itemize @bullet -@item -If you delete or move the compiled file after loading it, Emacs can no -longer load the remaining function definitions not already loaded. - -@item -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. -@end 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 non-@code{nil} 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: - -@example --*-byte-compile-dynamic: t;-*- -@end example - -@defvar byte-compile-dynamic -If this is non-@code{nil}, the byte compiler generates compiled files -that are set up for dynamic function loading. -@end defvar - -@defun 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}. -@end defun - -@node Eval During Compile -@section Evaluation During Compilation - - These features permit you to write code to be evaluated during -compilation of a program. - -@defspec eval-and-compile body@dots{} -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. - -@code{autoload} 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 -@code{eval-and-compile} 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 -@code{eval-and-compile} 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). -@end defspec - -@defspec eval-when-compile body@dots{} -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. - -@cindex compile-time constant -If you have a constant that needs some calculation to produce, -@code{eval-when-compile} can do that at compile-time. For example, - -@lisp -(defvar my-regexp - (eval-when-compile (regexp-opt '("aaa" "aba" "abb")))) -@end lisp - -@cindex 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, - -@lisp -(eval-when-compile - (require 'my-macro-package)) ;; only macros needed from this -@end 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, - -@lisp -(eval-when-compile - (unless (fboundp 'some-new-thing) - (defmacro 'some-new-thing () - (compatibility code)))) -@end lisp - -@noindent -This is often good for code that's only a fallback for compatibility -with other versions of Emacs. - -@strong{Common 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. -@end defspec - -@node Compiler Errors -@section Compiler Errors -@cindex compiler errors - - Byte compilation outputs all errors and warnings into the buffer -@samp{*Compile-Log*}. 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 -@code{fboundp} test, like this: - -@example -(if (fboundp '@var{func}) ...(@var{func} ...)...) -@end example - -@noindent -The call to @var{func} must be in the @var{then-form} of the -@code{if}, and @var{func} must appear quoted in the call to -@code{fboundp}. (This feature operates for @code{cond} as well.) - - Likewise, you can suppress a compiler warning for an unbound variable -@var{variable} by conditionalizing its use on a @code{boundp} test, -like this: - -@example -(if (boundp '@var{variable}) ...@var{variable}...) -@end example - -@noindent -The reference to @var{variable} must be in the @var{then-form} of the -@code{if}, and @var{variable} must appear quoted in the call to -@code{boundp}. - - You can suppress any compiler warnings using the construct -@code{with-no-warnings}: - -@c This is implemented with a defun, but conceptually it is -@c a special form. - -@defspec with-no-warnings body@dots{} -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. -@end defspec - -@node Byte-Code Objects -@section Byte-Code Function Objects -@cindex compiled function -@cindex byte-code function - - Byte-compiled functions have a special data type: they are -@dfn{byte-code 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: - -@table @var -@item arglist -The list of argument symbols. - -@item byte-code -The string containing the byte-code instructions. - -@item constants -The vector of Lisp objects referenced by the byte code. These include -symbols used as function names and variable names. - -@item stacksize -The maximum stack size this function needs. - -@item 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}). - -@item 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. -@end table - -Here's an example of a byte-code function object, in printed -representation. It is the definition of the command -@code{backward-sexp}. - -@example -#[(&optional arg) - "^H\204^F^@@\301^P\302^H[!\207" - [arg 1 forward-sexp] - 2 - 254435 - "p"] -@end example - - The primitive way to create a byte-code object is with -@code{make-byte-code}: - -@defun make-byte-code &rest elements -This function constructs and returns a byte-code function object -with @var{elements} as its elements. -@end 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. - -@node Disassembly -@section Disassembled Byte-Code -@cindex 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. - -@deffn 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 -@var{buffer-or-name} is non-@code{nil}, 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. -@end 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. - -@example -@group -(defun factorial (integer) - "Compute factorial of an integer." - (if (= 1 integer) 1 - (* integer (factorial (1- integer))))) - @result{} factorial -@end group - -@group -(factorial 4) - @result{} 24 -@end group - -@group -(disassemble 'factorial) - @print{} byte-code for factorial: - doc: Compute factorial of an integer. - args: (integer) -@end group - -@group -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.} -@end group - -@group -2 eqlsign ; @r{Pop top two values off stack,} - ; @r{compare them,} - ; @r{and push result onto stack.} -@end group - -@group -3 goto-if-nil 10 ; @r{Pop and test top of stack;} - ; @r{if @code{nil}, go to 10,} - ; @r{else continue.} -@end group - -@group -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).} -@end group - -@group -10 constant * ; @r{Push symbol @code{*} onto stack.} - -11 varref integer ; @r{Push value of @code{integer} onto stack.} -@end group - -@group -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.} -@end group - -@group - ; @r{Stack now contains:} - ; @minus{} @r{decremented value of @code{integer}} - ; @minus{} @r{@code{factorial}} - ; @minus{} @r{value of @code{integer}} - ; @minus{} @r{@code{*}} -@end group - -@group -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.} -@end group - -@group - ; @r{Stack now contains:} - ; @minus{} @r{result of recursive} - ; @r{call to @code{factorial}} - ; @minus{} @r{value of @code{integer}} - ; @minus{} @r{@code{*}} -@end group - -@group -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.} -@end group - -@group -17 return ; @r{Return the top element} - ; @r{of the stack.} - @result{} nil -@end group -@end example - -The @code{silly-loop} function is somewhat more complex: - -@example -@group -(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 -@end group - -@group -(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} - ; @r{@code{current-time-string}} - ; @r{onto top of stack.} -@end group - -@group -1 call 0 ; @r{Call @code{current-time-string}} - ; @r{ with no argument,} - ; @r{ pushing result onto stack.} -@end group - -@group -2 varbind t1 ; @r{Pop stack and bind @code{t1}} - ; @r{to popped value.} -@end group - -@group -3 varref n ; @r{Get value of @code{n} from} - ; @r{the environment and push} - ; @r{the value onto the stack.} -@end group - -@group -4 sub1 ; @r{Subtract 1 from top of stack.} -@end group - -@group -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.} -@end group - -@group -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.} -@end group - -@group -7 constant 0 ; @r{Push 0 onto stack.} -@end group - -@group -8 gtr ; @r{Pop top two values off stack,} - ; @r{test if @var{n} is greater than 0} - ; @r{and push result onto stack.} -@end group - -@group -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} -@end group - -@group -12 constant nil ; @r{Push @code{nil} onto stack} - ; @r{(this is the body of the loop).} -@end group - -@group -13 discard ; @r{Discard result of the body} - ; @r{of the loop (a while loop} - ; @r{is always evaluated for} - ; @r{its side effects).} -@end group - -@group -14 goto 3 ; @r{Jump back to beginning} - ; @r{of while loop.} -@end group - -@group -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.} -@end group - -@group -18 varref t1 ; @r{Push value of @code{t1} onto stack.} -@end group - -@group -19 constant current-time-string ; @r{Push} - ; @r{@code{current-time-string}} - ; @r{onto top of stack.} -@end group - -@group -20 call 0 ; @r{Call @code{current-time-string} again.} -@end group - -@group -21 list2 ; @r{Pop top two elements off stack,} - ; @r{create a list of them,} - ; @r{and push list onto stack.} -@end group - -@group -22 unbind 1 ; @r{Unbind @code{t1} in local environment.} - -23 return ; @r{Return value of the top of stack.} - - @result{} nil -@end group -@end example - - -@ignore - arch-tag: f78e3050-2f0a-4dee-be27-d9979a0a2289 -@end ignore |