Re: defmacro is worse than my neighbours cat

[Alan Mackenzie]

'Morning, Lennart!

On Fri, Sep 12, 2008 at 11:13:10PM +0200, Lennart Borgman (gmail) wrote:
> defmacro is worse than my neighbour's cat.

Miaow!!!

> When I think I everything is fine and I calm down they bite.

> I have a defmacro where I define a function and I want to build the doc
> string for this function in a certain way. This works fine - until I
> byte compile it. Can someone please try to explain to me how I can do
> what I want?

> Below is the defmacro. Look for "fix-me".


> (defmacro define-mumamo-multi-major-mode (fun-sym spec-doc chunks)
>   "Define a function that turn on support for multiple major modes."
>   (let* ((mumamo-describe-chunks (make-symbol "mumamo-describe-chunks"))

OK, here's a problem.  You have _two_ symbols called
"mumamo-describe-chunks" here.  One (uninterned) is the value of the
other.  Why do this?  Why not just declare the symbol directly inside the
let* form and use it?

You really don't need to use make-symbol at all, unless you deliberately
want it uninterned, or you're making up the name as you go along.  You
can simply write

   (let* mumamo-describe-chunks

>          (turn-on-fun (if (symbolp fun-sym)

>                           (symbol-value
>                            (intern
>                             (symbol-name (quote fun-sym))))

This bit seems crazy.  

    (symbol-name (quote fun-sym))

is easier to read as

    (symbol-name 'fun-sym)

which is "fun-sym".  You then "intern" it (i.e. get the (existing)
'fun-sym) and then take the value of 'fun-sym with `symbol-value'.

You don't need this.  You know that (the value of) fun-sym is a symbol,
so these three lines are entirely equivalent to

                            fun-sym

.  ;-)

>                         (error "Parameter FUN-SYM must be a symbol")))
>          (turn-on-fun-alias (intern
>                              (concat "mumamo-alias-"
>                                      (symbol-name
>                                       (symbol-value
>                                        (intern
>                                         (symbol-name (quote fun-sym))))))))

Here you've got one sensible use of intern, and one silly one.  This
should just say:

          (turn-on-fun-alias (intern (concat "mumamo-alias-" fun-sym)))

.  At least I think it should - it's a bit early at the moment.  ;-) 

I've got to get to bed, so I can't look at the rest right now.

>          (turn-on-hook (intern (concat (symbol-name turn-on-fun) "-hook")))
>          (turn-on-map  (intern (concat (symbol-name turn-on-fun) "-map")))
>          (turn-on-hook-doc (concat "Hook run at the very end of `"
>                                    (symbol-name turn-on-fun) "'."))
>          (chunks2 (if (symbolp chunks)
>                       (symbol-value chunks)
>                     chunks))
>          (docstring
>           (concat
>            spec-doc
>            "

> This function is called a multi major mode.  The main use for it
> is in `auto-mode-alist' to have Emacs do this setup whenever you
> open a file named in a certain way.  \(You can of course call
> this function directly yourself too.)

> It sets up for multiple mode in the following way:

> "
>            ;; Fix-me: During byte compilation the next line is not
>            ;; expanded as I thought because the functions in CHUNK is
>            ;; not defined. How do I fix this?
>            (funcall 'mumamo-describe-chunks chunks2)
>            "

> At the very end this multi major mode function runs first the hook
> `mumamo-turn-on-hook' and then `" (symbol-name turn-on-hook) "'.

> There is a keymap specific to this multi major mode, but it is
> not returned by `current-local-map' which returns the chunk's
> major mode's local keymap.

> The keymap is named `" (symbol-name turn-on-map) "'.

> This major mode has an alias `mumamo-alias-"
> (symbol-name turn-on-fun) "'.
> For more information see `define-mumamo-multi-major-mode'."
>            )))
>     `(progn
>        (add-to-list 'mumamo-defined-turn-on-functions (cons (car
> ',chunks2) ',turn-on-fun))
>        (defvar ,turn-on-hook nil ,turn-on-hook-doc)
>        (defvar ,turn-on-map (make-sparse-keymap)
>          ,(concat "Keymap for multi major mode function `"
>                   (symbol-name turn-on-fun) "'"))
>        (defvar ,turn-on-fun nil)
>        (make-variable-buffer-local ',turn-on-fun)
>        (put ',turn-on-fun 'permanent-local t)
>        (defun ,turn-on-fun nil ,docstring
>          (interactive)
>          (let ((old-major-mode (or mumamo-major-mode
>                                    major-mode)))
>            (kill-all-local-variables)
>            (run-hooks 'change-major-mode-hook)
>            (setq mumamo-multi-major-mode ',turn-on-fun)
>            (setq ,turn-on-fun t)
>            (mumamo-add-multi-keymap ',turn-on-fun ,turn-on-map)
>            (setq mumamo-current-chunk-family (copy-tree ',chunks2))
>            (mumamo-turn-on-actions old-major-mode)
>            (run-hooks ',turn-on-hook)))
>        (defalias ',turn-on-fun-alias ',turn-on-fun)
>        )))

-- 
Alan Mackenzie (Nuremberg, Germany).