Re: Best practices for writing services

[raingloom <raingloom@riseup.net>]

On Thu, 22 Apr 2021 09:19:56 +0200
Xinglu Chen <public@yoctocell.xyz> wrote:

> On Thu, Apr 22 2021, raingloom wrote:
> 
> >> One thing that I find a little annoying is that you have to
> >> specify a default value for the fields.  
> >
> > Are you sure? If you don't specify a default, won't the user just be
> > forced to write
> > (service whatever
> > 	(whatever-configuration
> > 		(mandatory-field 'bleepbloop)))
> >
> > instead of the shorter (service whatever)?  
> 
> If I write something like this
> 
> #+begin_src scheme
> (use-modules (gnu services configuration))
> (define (serialize-list field-name val) "")
> (define-configuration test-config
>   (config
>    (list)
>    "configuration for test"))
> #+end_src
> 
> and evaluate it, I will get an error.  I have to specify a default
> value for the ‘config’ field to make it work.
> 
> #+begin_src scheme
> (use-modules (gnu services configuration))
> (define (serialize-list field-name val) "")
> (define-configuration test-config
>   (config
>    (list '())                           ;default to '()
>    "configuration for test"))
> #+end_src
> 

Weird. I'd consider this a bug in define-configuration.
define-record-type* does not have this limitation.