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

[Clément Lassieur]

> +(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?