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Re: Trouble with eval-when-compile.
From: |
Helmut Eller |
Subject: |
Re: Trouble with eval-when-compile. |
Date: |
Wed, 31 Aug 2011 16:22:50 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.0.50 (gnu/linux) |
* Alan Mackenzie [2011-08-31 13:55] writes:
> Hi, everybody.
>
> Any chance of a tip?
>
> I have two files like this (grossly simplified, of course):
>
> when-compile-sub.el:
> (defconst str "Foo")
> (provide 'when-compile-sub)
>
> when-compile.el:
> (eval-when-compile
> (require 'when-compile-sub))
>
> (defconst strng `,str)
> (message "strng is %s" strng)
>
> I think it's clear what I want to do - that is, to (require
> when-compile-sub.elc) only at compile time, and use the value of a
> constant at runtime in the main file.
(defconst strng (eval-when-compile str))
would work better.
>
> Both files compile OK. But when I try to load when-compile.elc, with
>
> emacs -Q -batch -l when-compile.elc
>
> , I get the error message:
>
> Symbol's value as variable is void: str
>
> What is going on here?
`,str is rewritten to str
> str is merely a compile time constant. Why is
> anything about str still hanging around at runtime?
The value of a named constant is stored in the value slot of its symbol.
I guess that's less problematic with regard to eq-ness than dumping the
value to the .elc file and reconstructing it on load time.
Helmut