*** Welcome to IELM *** Type (describe-mode) for help.
ELISP> (defvar :k)
:k
ELISP> (defvar :k 1)
:k
ELISP> (defconst :k 1)
*** Eval error *** Attempt to set a constant symbol: :k
ELISP> (set :k :k)
:k
ELISP> (set :k 1)
*** Eval error *** Attempt to set a constant symbol: :k
ELISP> (set-default :k :k)
:k
ELISP> (set-default :k 1)
*** Eval error *** Attempt to set a constant symbol: :k
ELISP>
For consistency:
(defvar CONSTANT) ; should work
(defvar CONSTANT ITS-VALUE) ; should work
(defvar CONSTANT OTHER-VALUE) ; should fail
The attached patch implements this behavior. I'm calling error
directly, copying the error message from set_internal; another idea
would be to allow the call to Fset_default to go through when
NILP (tem) ||
(SYMBOL_CONSTANT_P (sym) && !EQ (tem, tail))
which avoid duplicating the error checking and the message, but
doesn't seem clean to me. Opinions?
--
/L/e/k/t/u
Index: src/eval.c
===================================================================
RCS file: /cvsroot/emacs/emacs/src/eval.c,v
retrieving revision 1.243
diff -u -2 -r1.243 eval.c
--- src/eval.c 23 Jun 2005 16:07:51 -0000 1.243
+++ src/eval.c 24 Jun 2005 03:42:47 -0000
@@ -793,4 +793,8 @@
if (NILP (tem))
Fset_default (sym, Feval (Fcar (tail)));
+ else if (SYMBOL_CONSTANT_P (sym)
+ && !EQ (tem, tail))
+ error ("Attempt to set a constant symbol: %s",
+ SDATA (SYMBOL_NAME (sym)));
else
{ /* Check if there is really a global binding rather than just a let
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