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Re: Macro Expansion Inconsistency
From: |
Nicolas Richard |
Subject: |
Re: Macro Expansion Inconsistency |
Date: |
Wed, 17 Dec 2014 11:04:58 +0100 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/25.0.50 (gnu/linux) |
Alexander Shukaev <haroogan@gmail.com> writes:
> I currently have the following macro baked:
>
> (defmacro bm-define-flag
> (name index character foreground)
> (let* ((symbol (intern (format "bm-%s-flag"
> (symbol-name name))))
> (character-symbol (intern (format "%s-character"
> (symbol-name symbol)))))
> (put symbol 'index index)
> (put symbol 'character character-symbol)
> (eval `(defcustom ,character-symbol
> ,character
> "Character for flag."
> :tag "BM Flag Character"
> :group 'buffer-manager
> :type 'character))
> (eval `(defface ,symbol
> `((t :foreground ,foreground
> :weight bold))
> "Face for flag."
> :tag "BM Flag Face"
> :group 'buffer-manager-faces))))
> [...]
> causes the error: (void-variable bm-xxx-flag) in `eval'
> [...]
> How to overcome it?
Quick'n'very-dirty : add nil or t (or anything that can be evaluated
twice safely) at the end of your macro definition.
> Do you have any further recommendations on this macro?
It's awful :) But don't worry : it's easy to write awful things, and
it's good that you post about it here.
In your case I'd point out these problems :
(i) it uses explicit eval for no good reason
(ii) it doesn't return code (that's the error you see)
(iii) it relies on dynamical binding (because of ',foreground' in a
second layer of quasi-quoting, which is only evalled by the explicit
eval.).
I think this works (lightly tested) :
(defmacro bm-define-flag (name index character foreground)
(let* ((symbol (intern (format "bm-%s-flag"
(symbol-name name))))
(character-symbol (intern (format "%s-character"
(symbol-name symbol)))))
(put symbol 'index index)
(put symbol 'character character-symbol)
`(progn ;; this is the code we're going to return after expansion.
;; Emacs will eval the whole progn form.
(defcustom ,character-symbol
,character
"Character for flag."
:tag "BM Flag Character"
:group 'buffer-manager
:type 'character)
(defface ,symbol
'((t :foreground ,foreground ;; the comma can be used,
;; even after normal quoting
:weight bold))
"Face for flag."
:tag "BM Flag Face"
:group 'buffer-manager-faces))))
If you'd like to read more about macros, I wrote about them at
http://lists.gnu.org/archive/html/help-gnu-emacs/2014-09/msg00473.html
(there's a typo in the first paragraph, apply
`sed s/evaluation time/expansion time/' please)
HTH,
--
Nicolas Richard
- Macro Expansion Inconsistency, Alexander Shukaev, 2014/12/16
- Re: Macro Expansion Inconsistency, Joost Kremers, 2014/12/16
- Re: Macro Expansion Inconsistency, Alexander Shukaev, 2014/12/16
- Re: Macro Expansion Inconsistency, John Mastro, 2014/12/16
- Re: Macro Expansion Inconsistency, Alexander Shukaev, 2014/12/16
- Re: Macro Expansion Inconsistency, Alexander Shukaev, 2014/12/16
- Re: Macro Expansion Inconsistency, Alexander Shukaev, 2014/12/16
- Re: Macro Expansion Inconsistency,
Nicolas Richard <=
- Re: Macro Expansion Inconsistency, Alexander Shukaev, 2014/12/17
- Re: Macro Expansion Inconsistency, Stefan Monnier, 2014/12/17
- Re: Macro Expansion Inconsistency, Alexander Shukaev, 2014/12/17
- Re: Macro Expansion Inconsistency, Nicolas Richard, 2014/12/17
- Re: Macro Expansion Inconsistency, Alexander Shukaev, 2014/12/17
- Re: Macro Expansion Inconsistency, Nicolas Richard, 2014/12/17
- Re: Macro Expansion Inconsistency, Alexander Shukaev, 2014/12/17
- Message not available
- Re: Macro Expansion Inconsistency, Barry Margolin, 2014/12/17
- Re: Macro Expansion Inconsistency, Alexander Shukaev, 2014/12/17
- Message not available
- Re: Macro Expansion Inconsistency, Rusi, 2014/12/16