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From: Taylan Kammer <taylan.kammer@gmail.com>
To: Damien Mattei <damien.mattei@gmail.com>, guile-devel@gnu.org
Subject: Re: new function
Date: Sun, 19 Sep 2021 23:38:59 +0200	[thread overview]
Message-ID: <147c2fb4-75d6-7cf6-4f4a-4edd996b0a4a@gmail.com> (raw)
In-Reply-To: <CADEOadfF+rR=fW0fS-PkQkDN8EHFB1sJnkeePMJyc23m9shLgA@mail.gmail.com>

On 19.09.2021 09:54, Damien Mattei wrote:
> hello,
> i'm developing an extension to Scheme
> and i need a procedure or macro that define a variable only if it is not bind and if it is just set! it.
> 
> I can not do it in Guile or any Scheme,and i'm desperately searching a way to do that. I finally conclude that it can be done only by adding it in the language.
> 
> Can someone include a such function in Guile next release?
> i know guile have a predicate defined? to test binfing of a vairable but writing a macro with it is not possible because define can be used in an expression context.
> 
> Thank in advance for any help
> Damien

What is the utility of such a function?  Since Scheme is lexically scoped,
it's generally obvious whether a variable has already been defined or not,
rendering such an operation useless.

If you're constructing code from outside input so that you don't know
whether a provided variable name represents a variable that's already been
defined or not, then you could use the module reflection API:

https://www.gnu.org/software/guile/manual/html_node/Module-System-Reflection.html

Sounds like 'module-define!' does exactly what you ask for.  I wonder what
exactly your use-case is though.  Chances are that your use-case is best
served with a simple data structure like a hash table...

-- 
Taylan



  parent reply	other threads:[~2021-09-19 21:38 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-19  7:54 new function Damien Mattei
2021-09-19 14:41 ` Matt Wette
2021-09-19 14:43   ` Matt Wette
2021-09-19 21:38 ` Taylan Kammer [this message]
2021-09-21 12:26   ` Damien Mattei
2021-09-22  8:44   ` Damien Mattei
2021-09-22  9:06     ` William ML Leslie
2021-09-22  9:53       ` Damien Mattei
2021-09-22 18:51         ` Taylan Kammer
2021-09-22 21:52           ` William ML Leslie
2021-09-23  8:40             ` Damien Mattei
2021-09-23 19:03             ` Taylan Kammer
2021-09-23 17:27           ` Damien Mattei
2021-09-23 18:00             ` Maxime Devos
2021-09-23 20:27             ` Taylan Kammer
2021-09-23 20:42               ` Damien Mattei
2021-09-23 20:48               ` Taylan Kammer
2021-09-23 21:53                 ` Damien Mattei
2021-09-24  4:41                   ` Damien Mattei

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