Subject: Re: bug#53663: [PATCH] gnu: services: Also accept 'undefined in maybe-foo? constructs.

From: Ludovic Courtès <[email-masked]>
Date: Tue, 01 Feb 2022 10:53:38 +0100

Hi!

Attila Lendvai <[email-masked]> skribis:

> This is a temporary bandaid until a more explicit handling of maybe types is
> introduced for configurations (e.g. by using srfi-189). Until then, with this
> change it becomes possible to have definitions like:
>
> (define-maybe string (no-serialization))
>
> (define-configuration my-configuration
>   (my-field (maybe-string))
>   (no-serialization))
>
> i.e. without providing a default value for MY-FIELD.
> ---
>  gnu/services/configuration.scm | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/gnu/services/configuration.scm b/gnu/services/configuration.scm
> index 0de350a4df..c5f276eab5 100644
> --- a/gnu/services/configuration.scm
> +++ b/gnu/services/configuration.scm
> @@ -141,7 +141,9 @@ (define (define-maybe-helper serialize? prefix syn)
>                                      (id #'stem #'serialize-maybe- #'stem))))
>         #`(begin
>             (define (maybe-stem? val)
> -             (or (eq? val 'disabled) (stem? val)))
> +             (or (eq? val 'disabled)
> +                 (eq? val 'undefined)
> +                 (stem? val)))

My understanding is that 'disabled is here precisely to allow users to
not provide a value, in which case the generated configuration file will
not contain anything for that field.

What would be different here?

Thanks,
Ludo’.