Re: isc-bind service draft

[Chris Marusich <cmmarusich@gmail.com>]

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Hi Oleg,

Chris Marusich <cmmarusich@gmail.com> writes:

>>
>> (define (emit-bind-options-config options)
>>   (match options
>>     (($ <bind-options-configuration> user _ run-directory pid-file
>>                                      listen-v4 listen-v6 listen-port
>>                                      allow-recursion? allow-transfer?
>>                                      allow-update?
>>                                      version hostname server-id)
>
> Some of these slots (e.g., listen-v4) appear to be un-used.  Instead of
> listing positional slots by name, maybe it would be better to bind the
> entire <bind-options-configuration> to a variable, and then use the
> accessor procedures (e.g., bind-options-configuration-listen-v4) to get
> just the attributes you need.  This has the benefit of being more
> resilient to refactorings which change the order of fields in the
> record, also.  I realize that a lot of the code in Guix relies on
> positional matching of slots like this, so I don't mind if you keep it
> as-is, but consider my suggestion as food for thought.

FYI, I just learned that there is a way to do this with pattern matching
in Guile.  You can write something like the following:

(match options
  ((? bind-options-configuration? (= bind-options-configuration-listen-v4 listen-v4))
   ;; Do something with listen-v4
   (foo listen-v4)))

As far as I know, this is the same as writing something like:

(match options
  ((? bind-options-configuration? opts)
   (let ((listen-v4 (bind-options-configuration-listen-v4 opts)))
     ;; Do something with listen-v4
     (foo listen-v4))))

-- 
Chris

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