+ Q4.7.1::).
+
+\1f
+File: xemacs-faq.info, Node: Q5.0.20, Next: Q5.1.1, Prev: Q5.0.19, Up: Miscellaneous
+
+Q5.0.20: Is there a way to start a new XEmacs if there's no gnuserv running, and otherwise use gnuclient?
+---------------------------------------------------------------------------------------------------------
+
+ Jan Vroonhof <vroonhof@math.ethz.ch> writes:
+ Here is one of the solutions, we have this in a script called
+ `etc/editclient.sh'.
+ #!/bin/sh
+ if gnuclient -batch -eval t >/dev/null 2>&1
+ then
+ exec gnuclient ${1+"$@"}
+ else
+ xemacs -unmapped -f gnuserv-start &
+ until gnuclient -batch -eval t >/dev/null 2>&1
+ do
+ sleep 1
+ done
+ exec gnuclient ${1+"$@"}
+ fi
+
+ Note that there is a known problem when running XEmacs and
+ 'gnuclient -nw' on the same TTY.
+
+\1f
+File: xemacs-faq.info, Node: Q5.1.1, Next: Q5.1.2, Prev: Q5.0.20, Up: Miscellaneous
+
+5.1: Emacs Lisp Programming Techniques
+======================================
+
+Q5.1.1: What is the difference in key sequences between XEmacs and GNU Emacs?
+-----------------------------------------------------------------------------
+
+ Erik Naggum <clerik@naggum.no> writes;
+
+ Emacs has a legacy of keyboards that produced characters with
+ modifier bits, and therefore map a variety of input systems into
+ this scheme even today. XEmacs is instead optimized for X events.
+ This causes an incompatibility in the way key sequences are
+ specified, but both Emacs and XEmacs will accept a key sequence as
+ a vector of lists of modifiers that ends with a key, e.g., to bind
+ `M-C-a', you would say `[(meta control a)]' in both Emacsen.
+ XEmacs has an abbreviated form for a single key, just (meta
+ control a). Emacs has an abbreviated form for the Control and the
+ Meta modifiers to string-characters (the ASCII characters), as in
+ `\M-\C-a'. XEmacs users need to be aware that the abbreviated
+ form works only for one-character key sequences, while Emacs users
+ need to be aware that the string-character is rather limited.
+ Specifically, the string-character can accommodate only 256
+ different values, 128 of which have the Meta modifier and 128 of
+ which have not. In each of these blocks, only 32 characters have
+ the Control modifier. Whereas `[(meta control A)]' differs from
+ `[(meta control a)]' because the case differs, `\M-\C-a' and
+ `\M-\C-A' do not. Programmers are advised to use the full common
+ form, both because it is more readable and less error-prone, and
+ because it is supported by both Emacsen.
+
+ Another (even safer) way to be sure of the key-sequences is to use
+the `read-kbd-macro' function, which takes a string like `C-c <up>',
+and converts it to the internal key representation of the Emacs you
+use. The function is available both on XEmacs and GNU Emacs.
+
+\1f
+File: xemacs-faq.info, Node: Q5.1.2, Next: Q5.1.3, Prev: Q5.1.1, Up: Miscellaneous
+
+Q5.1.2: Can I generate "fake" keyboard events?
+----------------------------------------------
+
+ I wonder if there is an interactive function that can generate
+"fake" keyboard events. This way, I could simply map them inside
+XEmacs.
+
+ This seems to work:
+
+ (defun cg--generate-char-event (ch)
+ "Generate an event, as if ch has been typed"
+ (dispatch-event (character-to-event ch)))
+
+ ;; Backspace and Delete stuff
+ (global-set-key [backspace]
+ (lambda () (interactive) (cg--generate-char-event 127)))
+ (global-set-key [unknown_keysym_0x4]
+ (lambda () (interactive) (cg--generate-char-event 4)))
+
+\1f
+File: xemacs-faq.info, Node: Q5.1.3, Next: Q5.1.4, Prev: Q5.1.2, Up: Miscellaneous
+
+Q5.1.3: Could you explain `read-kbd-macro' in more detail?
+----------------------------------------------------------
+
+ The `read-kbd-macro' function returns the internal Emacs
+representation of a human-readable string (which is its argument).
+Thus:
+
+ (read-kbd-macro "C-c C-a")
+ => [(control ?c) (control ?a)]
+
+ (read-kbd-macro "C-c C-. <up>")
+ => [(control ?c) (control ?.) up]
+
+ In GNU Emacs the same forms will be evaluated to what GNU Emacs
+understands internally--the sequences `"\C-x\C-c"' and `[3 67108910
+up]', respectively.
+
+ The exact "human-readable" syntax is defined in the docstring of
+`edmacro-mode'. I'll repeat it here, for completeness.
+
+ Format of keyboard macros during editing:
+
+ Text is divided into "words" separated by whitespace. Except for
+ the words described below, the characters of each word go directly
+ as characters of the macro. The whitespace that separates words is
+ ignored. Whitespace in the macro must be written explicitly, as in
+ `foo <SPC> bar <RET>'.
+
+ * The special words `RET', `SPC', `TAB', `DEL', `LFD', `ESC',
+ and `NUL' represent special control characters. The words
+ must be written in uppercase.
+
+ * A word in angle brackets, e.g., `<return>', `<down>', or
+ `<f1>', represents a function key. (Note that in the standard
+ configuration, the function key `<return>' and the control key
+ <RET> are synonymous.) You can use angle brackets on the
+ words <RET>, <SPC>, etc., but they are not required there.
+
+ * Keys can be written by their ASCII code, using a backslash
+ followed by up to six octal digits. This is the only way to
+ represent keys with codes above \377.
+
+ * One or more prefixes `M-' (meta), `C-' (control), `S-'
+ (shift), `A-' (alt), `H-' (hyper), and `s-' (super) may
+ precede a character or key notation. For function keys, the
+ prefixes may go inside or outside of the brackets: `C-<down>'
+ == `<C-down>'. The prefixes may be written in any order:
+ `M-C-x' == `C-M-x'.
+
+ Prefixes are not allowed on multi-key words, e.g., `C-abc',
+ except that the Meta prefix is allowed on a sequence of
+ digits and optional minus sign: `M--123' == `M-- M-1 M-2 M-3'.
+
+ * The `^' notation for control characters also works: `^M' ==
+ `C-m'.
+
+ * Double angle brackets enclose command names: `<<next-line>>'
+ is shorthand for `M-x next-line <RET>'.
+
+ * Finally, `REM' or `;;' causes the rest of the line to be
+ ignored as a comment.
+
+ Any word may be prefixed by a multiplier in the form of a decimal
+ number and `*': `3*<right>' == `<right> <right> <right>', and
+ `10*foo' == `foofoofoofoofoofoofoofoofoofoo'.
+
+ Multiple text keys can normally be strung together to form a word,
+ but you may need to add whitespace if the word would look like one
+ of the above notations: `; ; ;' is a keyboard macro with three
+ semicolons, but `;;;' is a comment. Likewise, `\ 1 2 3' is four
+ keys but `\123' is a single key written in octal, and `< right >'
+ is seven keys but `<right>' is a single function key. When in
+ doubt, use whitespace.
+
+\1f
+File: xemacs-faq.info, Node: Q5.1.4, Next: Q5.1.5, Prev: Q5.1.3, Up: Miscellaneous
+
+Q5.1.4: What is the performance hit of `let'?
+---------------------------------------------
+
+ In most cases, not noticeable. Besides, there's no avoiding
+`let'--you have to bind your local variables, after all. Some pose a
+question whether to nest `let's, or use one `let' per function. I
+think because of clarity and maintenance (and possible future
+implementation), `let'-s should be used (nested) in a way to provide
+the clearest code.
+
+\1f
+File: xemacs-faq.info, Node: Q5.1.5, Next: Q5.1.6, Prev: Q5.1.4, Up: Miscellaneous
+
+Q5.1.5: What is the recommended use of `setq'?
+----------------------------------------------
+
+ * Global variables
+
+ You will typically `defvar' your global variable to a default
+ value, and use `setq' to set it later.
+
+ It is never a good practice to `setq' user variables (like
+ `case-fold-search', etc.), as it ignores the user's choice
+ unconditionally. Note that `defvar' doesn't change the value of a
+ variable if it was bound previously. If you wish to change a
+ user-variable temporarily, use `let':
+
+ (let ((case-fold-search nil))
+ ... ; code with searches that must be case-sensitive
+ ...)
+
+ You will notice the user-variables by their docstrings beginning
+ with an asterisk (a convention).
+
+ * Local variables
+
+ Bind them with `let', which will unbind them (or restore their
+ previous value, if they were bound) after exiting from the `let'
+ form. Change the value of local variables with `setq' or whatever
+ you like (e.g. `incf', `setf' and such). The `let' form can even
+ return one of its local variables.
+
+ Typical usage:
+
+ ;; iterate through the elements of the list returned by
+ ;; `hairy-function-that-returns-list'
+ (let ((l (hairy-function-that-returns-list)))
+ (while l
+ ... do something with (car l) ...
+ (setq l (cdr l))))
+
+ Another typical usage includes building a value simply to work
+ with it.
+
+ ;; Build the mode keymap out of the key-translation-alist
+ (let ((inbox (file-truename (expand-file-name box)))
+ (i 0))
+ ... code dealing with inbox ...
+ inbox)
+
+ This piece of code uses the local variable `inbox', which becomes
+ unbound (or regains old value) after exiting the form. The form
+ also returns the value of `inbox', which can be reused, for
+ instance:
+
+ (setq foo-processed-inbox
+ (let .....))
+
+\1f
+File: xemacs-faq.info, Node: Q5.1.6, Next: Q5.1.7, Prev: Q5.1.5, Up: Miscellaneous
+
+Q5.1.6: What is the typical misuse of `setq' ?
+----------------------------------------------
+
+ A typical misuse is probably `setq'ing a variable that was meant to
+be local. Such a variable will remain bound forever, never to be
+garbage-collected. For example, the code doing:
+
+ (defun my-function (whatever)
+ (setq a nil)
+ ... build a large list ...
+ ... and exit ...)
+
+ does a bad thing, as `a' will keep consuming memory, never to be
+unbound. The correct thing is to do it like this:
+
+ (defun my-function (whatever)
+ (let (a) ; default initialization is to nil
+ ... build a large list ...
+ ... and exit, unbinding `a' in the process ...)
+
+ Not only is this prettier syntactically, but it makes it possible for
+Emacs to garbage-collect the objects which `a' used to reference.
+
+ Note that even global variables should not be `setq'ed without
+`defvar'ing them first, because the byte-compiler issues warnings. The
+reason for the warning is the following:
+
+ (defun flurgoze nil) ; ok, global internal variable
+ ...
+
+ (setq flurghoze t) ; ops! a typo, but semantically correct.
+ ; however, the byte-compiler warns.
+
+ While compiling toplevel forms:
+ ** assignment to free variable flurghoze
+
+\1f
+File: xemacs-faq.info, Node: Q5.1.7, Next: Q5.1.8, Prev: Q5.1.6, Up: Miscellaneous
+
+Q5.1.7: I like the `do' form of cl, does it slow things down?
+-------------------------------------------------------------
+
+ It shouldn't. Here is what Dave Gillespie has to say about cl.el
+performance:
+
+ Many of the advanced features of this package, such as `defun*',
+ `loop', and `setf', are implemented as Lisp macros. In
+ byte-compiled code, these complex notations will be expanded into
+ equivalent Lisp code which is simple and efficient. For example,
+ the forms
+
+ (incf i n)
+ (push x (car p))
+
+ are expanded at compile-time to the Lisp forms
+
+ (setq i (+ i n))
+ (setcar p (cons x (car p)))
+
+ which are the most efficient ways of doing these respective
+ operations in Lisp. Thus, there is no performance penalty for
+ using the more readable `incf' and `push' forms in your compiled
+ code.
+
+ _Interpreted_ code, on the other hand, must expand these macros
+ every time they are executed. For this reason it is strongly
+ recommended that code making heavy use of macros be compiled. (The
+ features labelled "Special Form" instead of "Function" in this
+ manual are macros.) A loop using `incf' a hundred times will
+ execute considerably faster if compiled, and will also
+ garbage-collect less because the macro expansion will not have to
+ be generated, used, and thrown away a hundred times.
+
+ You can find out how a macro expands by using the `cl-prettyexpand'
+ function.
+
+\1f
+File: xemacs-faq.info, Node: Q5.1.8, Next: Q5.1.9, Prev: Q5.1.7, Up: Miscellaneous
+
+Q5.1.8: I like recursion, does it slow things down?
+---------------------------------------------------
+
+ Yes. Emacs byte-compiler cannot do much to optimize recursion. But
+think well whether this is a real concern in Emacs. Much of the Emacs
+slowness comes from internal mechanisms such as redisplay, or from the
+fact that it is an interpreter.
+
+ Please try not to make your code much uglier to gain a very small
+speed gain. It's not usually worth it.