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Re: What's the equivalent of `boundp' for lexical variables?
From: |
tomas |
Subject: |
Re: What's the equivalent of `boundp' for lexical variables? |
Date: |
Sat, 27 Jan 2024 07:21:05 +0100 |
On Fri, Jan 26, 2024 at 08:16:46PM +0000, Alan Mackenzie wrote:
> Hello, Emacs.
>
> I have a problem in a macro, where I have the expression ,expr. I want
> to evaluate it, but get the error message void-variable (expr).
>
> In the good old days, I could have tested this with
>
> (if (boundp 'expr) (eval ,expr))
>
> , but now, with lexical variables, I can't find the equivalent to boundp.
> Is there such a facility for lexical variables, and if so what is it?
To offer something which might be half-right, but less whimsical
than the typical Andreas's answers: lexical variables are only
"known" at compile time (something to bear in mind when building
your macro; I take you know that). But functions, like "boundp"
take a symbol at run time and query it. The whole compile-time
"world" is now somewhere under the Atlantic Ocean and only
legends talk about it :-)
One work-around would be "ignore-errors" (I take this is roughly
what Common Lispers do). Assume lexical bindings, assume foo hasn't
been defined:
(ignore-errors foo)
=> nil
(let ((foo 12))
(ignore-errors foo))
=> 12
(Ignore-errors is a macro, so it gets expanded when useful to you)
Perhaps there's a solution along these lines.
Cheers, hth
--
tomás
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Re: What's the equivalent of `boundp' for lexical variables?,
tomas <=