Re: new function

[Taylan Kammer]

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