Re: Syntactic Diabetes (was Re: A friendlier API for operating-system declarations)

[Liliana Marie Prikler <liliana.prikler@gmail.com>]

Am Freitag, dem 24.11.2023 um 22:43 +0100 schrieb Edouard Klein:
> Dear Guixers,
> 
> Here is a quick status update on my proposition to expose composable
> functions to change operating-system declarations.
> 
> Thank you all for the feedback you gave me :) It's very nice to not
> be talking in the void.
> 
> After Liliana opined that these functions should not put too much
> burden on the maintainers, a position with which I wholeheartedly
> agree, here is what I came up with:
> 
> https://gitlab.com/edouardklein/guix/-/blob/beaverlabs/beaver/functional-services.scm
> 
> (file copied at the end of this email to make the list self-content
> instead of relying on external services)
> 
> That's a macro-writing macro called "define-os-macros-for" that, for
> any service (for example nginx), defines five forms. They all
> evaluate to a modified os:
> 
> (.nginx os)  ;; Add nginx in its default configuration
> (.nginx os toto titi tutu... )  ;; Add nginx, with toto... given as
> arguments to nginx-configuration
> (+nginx os toto titi tutu...)  ;; Extend an existing nginx service,
> giving
> toto... as arguments to simple-service
> (~nginx os toto...)  ;; Edit an existing nginx service, passing
> toto... as
> arguments to modify-service
> (-nginx os)  ;; Removes nginx
> 
> You can see all of them used in:
> https://gitlab.com/edouardklein/guix/-/blob/beaverlabs/beaver/system.scm?ref_type=heads
> 
> e.g. the mkdir-p function is a (+activation ...),
> all web server functions use (+nginx...),
> mumble is (.mumble... ),
> os/git uses (~openssh... ).
> 
> I've use (-foo) forms while testing, but not in production. The
> others are currently running in prod on guix-hosting.com and the-
> dam.org.
The naming is a little confusing and imho not clearly helpful.  For
example, why (.nginx os) instead of the triple

(service+ OS SERVICE [CONF])
(service- OS SERVICE)
(modify-service OS SERVICE UPDATE)

Of course, you could also define triples (add-SERVICE OS [CONF]), 
(remove-SERVICE OS) and (modify-SERVICE OS UPDATE), which would fall in
line with the macro approach, but keep names a little more readable. 
(If you want to use your names, you can rename them in #:use-modules).

> -----------------functional-services.scm----------------
> (define-module (beaver functional-services)
>    #:use-module (gnu system)
>    #:export (*-append))
> 
> (define (syntax->string s)
>   "Shorthand to convert a piece of syntax to a string"
>   (symbol->string (syntax->datum s)))
Or (compose symbol->string syntax->datum).

> (define (*->string s)
>   "Convert into a string any symbol-like type we may encounter in a
> macro"
>   (cond
>    [(string? s) s]
>    [(symbol? s) (symbol->string s)]
>    [else (syntax->string s)]))  ;; assume syntax
There should not be a need to define this.  Try to use exact types.

> (define* (*-append #:rest args)
>   "Return a symbol which is a concatenation of the given symbol-like
> args"
>   (string->symbol (apply string-append (map *->string args))))
As above.

> (define-syntax define-os-macros-for
>   ;; This macro, called like e.g. (define-os-macros-for foo) will
> define four
>   ;; forms, .foo, +foo, ~foo and -foo
>   ;;
>   ;; These forms take an operating-system as their first argument,
> and
>   ;; evaluate to an operating-system, which allows one to compose
> them
>   ;; (e.g. (foo (bar os))).
>   (lambda (x)
>     (syntax-case x ()
>       [(_ foo)
>        (with-syntax
>         ([dot-foo           (datum->syntax x (*-append "." #'foo))]
>          [plus-foo          (datum->syntax x (*-append "+" #'foo))]
>          [tilde-foo         (datum->syntax x (*-append "~" #'foo))]
>          [minus-foo         (datum->syntax x (*-append "-" #'foo))]
>          [foo-service-type  (datum->syntax x (*-append #'foo "-
> service-type"))]
>          [foo-configuration (datum->syntax x (*-append #'foo "-
> configuration"))])
You're repeating datum->syntax here a bit too much for my liking.

This patch is also missing the most important part of beaverlabs to
make this work: the -> threading macro.

Cheers