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[bug#43159] [PATCH 1/2] scripts: Use 'define-command' and have 'guix hel

From: Ludovic Courtès
Subject: [bug#43159] [PATCH 1/2] scripts: Use 'define-command' and have 'guix help' use that.
Date: Sun, 13 Sep 2020 15:03:04 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux)


Maxim Cournoyer <> skribis:

> Sorry I couldn't reply faster.

No problem.  I went ahead with this patch series, but nothing’s set in
stone and I’m open to further changes.

> Thanks for the detailed measurements!  It does indeed seem your approach
> is better, especially considering memory usage.  Perhaps the commands
> could have been moved to dedicated modules not using much dependency at
> all so that their closure would have been small hence fast to load, but
> keeping the commands definitions local to where they are useful is
> definitely a nice property.

We can’t really reduce the closure of commands.  In particular, (guix
scripts system) has to load pretty much “everything”.

What we could do is use #:autoload aggressively in the (guix scripts …)
modules, such that startup time would be as small as possible—e.g.,
‘--help’ would not trigger loading of a zillion modules.

It’s a bit tedious though and not necessarily helpful in the general
case where one is doing something non-trivial with the command.  Well
dunno, we could try!

>> In summary, while this approach undoubtedly looks awkward to any Lisper,
>> I think it’s a good way to not contribute to the general impression of
>> sluggishness and resource-hungriness of ‘guix’ commands.  :-)
>>>> +  (define (display-commands commands)
>>>> +    (let* ((names     (map (lambda (command)
>>>> +                             (string-join (command-name command)))
>>>> +                           commands))
>>>> +           (max-width (reduce max 0 (map string-length names))))
>>> You can drop reduce and use (max (map string-length names)) instead.
>> I could do (apply max (map …)) but I don’t like the idea of abusing
>> variadic argument lists in that way—I know, it’s very subjective.  ;-)
> Eh, I wonder why?  I may be missing something, but if max allows it,
> doesn't it mean it's a valid use?  Anyway, just curious to know what are
> the grounds for this personal preference :-).

It’s mostly aesthetic, but it comes from the idea that there could be
limitations on the maximum number of arguments a procedure can take, or
inefficiencies with dealing with many arguments.  Now, in today’s Guile,
there are no such issues…  (And now I look really silly!)  :-)


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