Re: [PATCH 3/3] gnu: Add CUPS service.

[Andy Wingo <wingo@igalia.com>]

On Mon 10 Oct 2016 10:32, Clément Lassieur <clement@lassieur.org> writes:

>> +(define-record-type* <configuration-field>
>> +  configuration-field make-configuration-field configuration-field?
>> +  (name configuration-field-name)
>> +  (type configuration-field-type)
>> +  (getter configuration-field-getter)
>> +  (predicate configuration-field-predicate)
>> +  (serializer configuration-field-serializer)
>> +  (default-value-thunk configuration-field-default-value-thunk)
>> +  (documentation configuration-field-documentation))
>> +
>> +(define-syntax define-configuration
>> +  (lambda (stx)
>> +    (define (id ctx part . parts)
>> +      (let ((part (syntax->datum part)))
>> +        (datum->syntax
>> +         ctx
>> +         (match parts
>> +           (() part)
>> +           (parts (symbol-append part
>> +                                 (syntax->datum (apply id ctx parts))))))))
>> +    (syntax-case stx ()
>> +      ((_ stem (field (field-type def) doc) ...)
>> +       (with-syntax (((field-getter ...)
>> +                      (map (lambda (field)
>> +                             (id #'stem #'stem #'- field))
>> +                           #'(field ...)))
>> +                     ((field-predicate ...)
>> +                      (map (lambda (type)
>> +                             (id #'stem type #'?))
>> +                           #'(field-type ...)))
>> +                     ((field-serializer ...)
>> +                      (map (lambda (type)
>> +                             (id #'stem #'serialize- type))
>> +                           #'(field-type ...))))
>> +           #`(begin
>> +               (define-record-type* #,(id #'stem #'< #'stem #'>)
>> +                 stem #,(id #'stem #'make- #'stem) #,(id #'stem #'stem #'?)
>> +                 (field field-getter (default def))
>> +                 ...)
>> +               (define #,(id #'stem #'stem #'-fields)
>> +                 (list (configuration-field
>> +                        (name 'field)
>> +                        (type 'field-type)
>> +                        (getter field-getter)
>> +                        (predicate field-predicate)
>> +                        (serializer field-serializer)
>> +                        (default-value-thunk (lambda () def))
>> +                        (documentation doc))
>> +                       ...))))))))
>> +
>> +(define (serialize-configuration config fields)
>> +  (for-each (lambda (field)
>> +              ((configuration-field-serializer field)
>> +               (configuration-field-name field)
>> +               ((configuration-field-getter field) config)))
>> +            fields))
>> +
>> +(define (validate-configuration config fields)
>> +  (for-each (lambda (field)
>> +              (let ((val ((configuration-field-getter field) config)))
>> +                (unless ((configuration-field-predicate field) val)
>> +                  (cups-configuration-field-error
>> +                   (configuration-field-name field) val))))
>> +            fields))
>
> These definitions are also in the Dovecot service. Would it make sense
> to put them in a place where they could be accessible from other
> services as well, thus avoiding code repetition?

Yes, it's a good idea.  I was holding off doing it until the third
service that used them, though, just to avoid prematurely making an
abstraction that might be the wrong thing; dunno.  WDYT?

Andy