Re: new function

[Matt Wette <matt.wette@gmail.com>]

On 9/19/21 7:41 AM, Matt Wette wrote:
> On 9/19/21 12:54 AM, 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
>
> Check the manual.
>
> scheme@(guile-user)> (define-once a 1)
> scheme@(guile-user)> (define-once a 2)
> scheme@(guile-user)> a
> $1 = 1
> scheme@(guile-user)>
>

Sorry.  I misread your post.   How about this:

mwette$ guile
scheme@(guile-user)> (define-once a 1)
scheme@(guile-user)> (define-once a 2)
scheme@(guile-user)> a
$1 = 1

scheme@(guile-user)> (define a 1)
scheme@(guile-user)> (define a 2)
scheme@(guile-user)> a
$2 = 2
scheme@(guile-user)>