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Re: problem with text properties whose names aren't symbols


From: Andreas Schwab
Subject: Re: problem with text properties whose names aren't symbols
Date: Mon, 12 Dec 2005 12:04:12 +0100
User-agent: Gnus/5.110003 (No Gnus v0.3) Emacs/22.0.50 (gnu/linux)

Joe Corneli <address@hidden> writes:

>>From the elisp manual (node: Text Properties):
>
>    Each property has a name and a value.  Both of these
>    can be any Lisp object, but the name is normally a symbol.
>
> Well, it seems that when the Lisp object is not a symbol,
> there is a problem.  This is illustrated by evaluating
> the following form interactively:
>
> (progn
>   (put-text-property (point) (1+ (point)) 
>                      '(example name)
>                       t)
>   (put-text-property (point) (1+ (point)) 
>                      '(example name)
>                       nil)
>   (text-properties-at (point)))

This is not a bug, because '(example name) and '(example name) are
distinct objects:

ELISP> (eq '(example name) '(example name))
nil

Try this instead:

(let ((name '(example name)))
  (put-text-property (point) (1+ (point)) name t)
  (put-text-property (point) (1+ (point)) name nil)
  (text-properties-at (point)))

Andreas.

-- 
Andreas Schwab, SuSE Labs, address@hidden
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
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