[bug#63985] [PATCH v3 02/11] services: configuration: Use transducers within serialize-configuration. (was : bug#63985: [PATCH RFC 0/5] Generic INI serializer & SRFI-171 for define-configuration)

[Maxim Cournoyer <maxim.cournoyer@gmail.com>]

Hello,

Bruno Victal <mirai@makinata.eu> writes:

> On 2023-10-02 18:25, Maxim Cournoyer wrote:
>> Bruno Victal <mirai@makinata.eu> writes:
>>> diff --git a/gnu/services/telephony.scm b/gnu/services/telephony.scm
>>> index 23ccb8d403..56b7772f58 100644
>>> --- a/gnu/services/telephony.scm
>>> +++ b/gnu/services/telephony.scm
>>> @@ -204,22 +205,20 @@ (define (jami-account->alist jami-account-object)
>>>        ('rendezvous-point? "Account.rendezVous")
>>>        ('peer-discovery? "Account.peerDiscovery")
>>>        ('bootstrap-hostnames "Account.hostname")
>>> -      ('name-server-uri "RingNS.uri")
>>> -      (_ #f)))
>>> +      ('name-server-uri "RingNS.uri")))
>>>  
>>> -  (filter-map (lambda (field)
>>> -                (and-let* ((name (field-name->account-detail
>>> +  (define jami-account-transducer
>>> +    (compose (tremove empty-serializer?)
>>> +             (tfilter-maybe-value jami-account-object)
>>> +             (tmap (lambda (field)
>>> +                     (let* ((name (field-name->account-detail
>>>                                    (configuration-field-name field)))
>>> -                           (value ((configuration-field-serializer field)
>>> -                                   name ((configuration-field-getter field)
>>> -                                         jami-account-object)))
>>> -                           ;; The define-maybe default serializer produces an
>>> -                           ;; empty string for unspecified values.
>>> -                           (value* (if (string-null? value)
>>> -                                       #f
>>> -                                       value)))
>>> -                  (cons name value*)))
>>> -              jami-account-fields))
>>> +                            (value ((configuration-field-serializer field)
>>> +                                    name ((configuration-field-getter field)
>>> +                                          jami-account-object))))
>>> +                       (cons name value))))))
>>> +
>>> +  (list-transduce jami-account-transducer rcons jami-account-fields))
>> 
>> Could you please state in a comment under "(define
>> jami-account-transducer" why the base transducer doesn't suffice?  It
>> isn't obvious to me from a casual inspection.  I guess it's because
>> base-transducer is not recursive?  Should it be?
>
> This is because you're changing the field names of the JAMI-ACCOUNT record type
> through `field-name->account-detail'.
> Conventional serializers are (serializer (field-name value)) procedures and this is
> how `base-transducer' calls them. Here you want to do something of the sort
> (serializer (translate-field-name name) value) so a custom transducer was written to
> account for this detour.
>
> I wonder if we could simply this with some functional programming as discussed in
> [1] instead.
>
>>>  (test-equal "symbol maybe value serialization, unspecified"
>>>    ""
>>> -  (gexp->approximate-sexp
>>> +  (eval-gexp
>>>     (serialize-configuration (config-with-maybe-symbol)
>>>                              config-with-maybe-symbol-fields)))
>> 
>> That's nice, though I don't understand why gexp->approximate needs to be
>> turned into eval-gexp?
>
> Using `gexp->approximate-sexp' alone doesn't result in a evaluation of the
> serialization process so eval-gexp has to be used in order to actually perform
> this test.

Great, thanks for the explanations!

-- 
Thanks,
Maxim