From: Arthur Miller <arthur.miller@live.com>
To: Michael Heerdegen <michael_heerdegen@web.de>
Cc: help-gnu-emacs@gnu.org
Subject: Re: Eval keymapp in a macros
Date: Thu, 12 Aug 2021 22:28:59 +0200 [thread overview]
Message-ID: <AM9PR09MB49771FC22BD96C925883DC1096F99@AM9PR09MB4977.eurprd09.prod.outlook.com> (raw)
In-Reply-To: <87zgtvns7x.fsf@web.de> (Michael Heerdegen's message of "Fri, 06 Aug 2021 05:54:10 +0200")
Michael Heerdegen <michael_heerdegen@web.de> writes:
Sorry for the little bit late answer. I didn't had time to look at this
immidiately, and then it just was left.
> Arthur Miller <arthur.miller@live.com> writes:
>
>> > And instead of `eval' better use `bound-and-true-p' - you know that you
>> > look at a symbol.
>>
>> Thanks. I can remove at least the eval in test with bound-and-true-p,
>> but I don't think I can remove the second eval, since I have to get
>> object the symbol is representing.
>
> And exactly this is what `bound-and-true-p' returns. But that doesn't
Aha, I did a little bit of a noob thing there, and didn't checked the
docs. Just expected return to be a boolean and forgott that in elisp,
actually lots of stuff return the object itself, which is handy (like
`or', or `and' etc).
> matter if you are actually having a problem like this:
>
>> However I am getting false positives from keymapp, it accepts anything
>> seems like:
>>
>> (defmacro with-key-map (mapname &rest body)
>> `(dolist (def '(,@body))
>> (define-key ,mapname
>> (if (vectorp (car def)) (car def)
>> (read-kbd-macro (car def)))
>> (if `(bound-and-true-p ,(cdr def))
>> (if `(keymapp ,(cdr def))
>> (eval (cdr def))
>> (cdr def))))))
>>
>> Instead I have to use to test for listp and functionp first:
>>
>> (defmacro with-key-map (mapname &rest body)
>> `(dolist (def '(,@body))
>> (define-key ,mapname
>> (if (vectorp (car def)) (car def)
>> (read-kbd-macro (car def)))
>> (if `(bound-and-true-p ,(cdr def))
>> (if (or (listp (cdr def))
>> (functionp (cdr def)))
>> (cdr def)
>> (if `(keymapp ,(cdr def))
>> (eval (cdr def))))))))
>>
>> And I can also remove last if, and just leave eval, keymapp does not
>> seems to cull anything out.
>
> I think you have a problem here with these nested backquotes, not
> everything you think gets evaluated. Have a look at the expansion
> (`macroexpand').
>
>> Anyway, thanks you for the help and feedback. I do have some better
>> understanding after this.
>
> An honest opinion: Maybe the advice to start with a function is the best
> one so far. Else you will be wasting time for nothing. Don't write
> macro code and look what happens when you call it and then try to fix
> what seems to be wrong. You'll get crazy and not learn very much. That
> approach doesn't work for most human brains.
Yes, that is a very good advice, if anyone else than me is reading this
in the future.
> One cool trick for learning: make the macro expander a named function.
>
> I'm using your first definition from above - it is equivalent to
>
> #+begin_src emacs-lisp
> (defmacro with-key-map (mapname &rest body)
> (apply #'my-with-key-map-expander mapname body))
>
> (defun my-with-key-map-expander (mapname &rest body)
> `(dolist (def '(,@body))
> (define-key ,mapname
> (if (vectorp (car def)) (car def)
> (read-kbd-macro (car def)))
> (if `(bound-and-true-p ,(cdr def))
> (if (or (listp (cdr def))
> (functionp (cdr def)))
> (cdr def)
> (if `(keymapp ,(cdr def))
> (eval (cdr def))))))))
> #+end_src
>
> While this is semantically exactly the same and doesn't make much of a
> difference you can now better study what the expander does: how it
> transforms code (or forms) to code (to be evaluated).
>
> E.g. now
>
> (with-key-map global-map ([f1] . make-frame-command))
>
> will internally use an ordinary function call:
>
> (my-with-key-map-expander 'global-map '([f1] . emacs-list-mode-map))
>
> to generate the expansion. You can use the debugger, study the return
> value etc. Why does the code it returns not work as expected? Would
> you write the code like that?
>
> To repeat: this is actually working in the wrong direction. Better
> start from the expected expansion, and then write an expander function
> that generates that expansion.
Indeed, and I agree. That was something like that I meant when I answered
in some earlier mail to Stefan. Anyway It all start with simple 6 lines
of very simple macro which worked out straightforward, so I was all the
time just "hacking" a single case it didn't worked for. But yes, in the
end, it is not very good approach.
Thank you for the help.
next prev parent reply other threads:[~2021-08-12 20:28 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-02 12:16 Eval keymapp in a macros Arthur Miller
2021-08-02 20:33 ` Michael Heerdegen
2021-08-02 20:53 ` [External] : " Drew Adams
2021-08-03 21:20 ` Arthur Miller
2021-08-04 0:18 ` Michael Heerdegen
2021-08-04 10:52 ` Arthur Miller
2021-08-04 23:56 ` Michael Heerdegen
2021-08-05 6:03 ` Arthur Miller
2021-08-06 3:54 ` Michael Heerdegen
2021-08-12 20:28 ` Arthur Miller [this message]
2021-08-04 4:54 ` Yuri Khan
2021-08-04 9:38 ` Arthur Miller
2021-08-04 15:37 ` Stefan Monnier via Users list for the GNU Emacs text editor
2021-08-05 6:12 ` Arthur Miller
2021-08-05 13:53 ` Stefan Monnier
2021-08-05 16:04 ` Arthur Miller
2021-08-05 16:34 ` Stefan Monnier
2021-08-06 4:17 ` Michael Heerdegen
2021-08-12 20:21 ` Arthur Miller
2021-08-05 0:03 ` Michael Heerdegen
2021-08-05 6:15 ` Arthur Miller
2021-08-06 3:18 ` Michael Heerdegen
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