From mboxrd@z Thu Jan  1 00:00:00 1970
From: ludo@gnu.org (Ludovic =?utf-8?Q?Court=C3=A8s?=)
Subject: Re: [PATCH 2/2] emacs: Add 'guix-package-from-file' command.
Date: Sun, 08 May 2016 20:40:58 +0200
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In-Reply-To: <1462704662-18972-3-git-send-email-alezost@gmail.com> (Alex
	Kost's message of "Sun, 8 May 2016 13:51:02 +0300")
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To: Alex Kost <alezost@gmail.com>
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Alex Kost <alezost@gmail.com> skribis:

> * emacs/guix-main.scm (register-package, packages-from-file): New procedu=
res.
> (%patterns-makers): Add 'from-file' search type.
> * emacs/guix-messages.el (guix-messages): Add messages for it.
> * emacs/guix-ui-package.el (guix-package-from-file): New command.
> (guix-package-info-insert-location): Adjust for 'from-file' type.
> * doc/emacs.texi (Emacs Commands): Document it.

[...]

> +@item M-x guix-package-from-file
> +Display package that the code within the specified file evaluates to.
> +@xref{Invoking guix package, @code{--install-from-file}}, for an example
> +of how a file may look like.

s/how a file/what such a file/

> +(define-values (package-by-address
> +                register-package)
> +  (let* ((table (delay (fold-packages
> +                        (lambda (package table)
> +                          (vhash-consq (object-address package)
> +                                       package table))
> +                        vlist-null)))
> +         (table* (lambda ()
> +                   (if (promise? table)
> +                       (force table)
> +                       table))))

It may be easier to always make =E2=80=98table=E2=80=99 a promise=E2=80=A6

> +    (values
> +     (lambda (address)
> +       "Return package by its object ADDRESS."
> +       (match (vhash-assq address (table*))
> +         ((_ . package) package)
> +         (_ #f)))
> +     (lambda (package)
> +       "Register PACKAGE by its 'object-address', so that later
> +'package-by-address' can be used to access it."
> +       (set! table
> +             (vhash-consq (object-address package)
> +                          package (table*)))))))

=E2=80=A6 by wrapping =E2=80=98vhash-consq=E2=80=99 in =E2=80=98delay=E2=80=
=99.

I think this approach is OK.

The rest LGTM!

To avoid =E2=80=98set!=E2=80=99 above, the options that come to mind would =
be:

  1. To not provide M-x guix-package-from-file and instead provide, say,
     M-x guix-install-package-from-file.  That way, we wouldn=E2=80=99t nee=
d to
     remember the package.

  2. To thread the state, consisting mainly of lookup tables/procedures,
     through the state monad, and to change the state in this particular
     case.

     Converting to this new style would be quite a bit of work, for just
     this one special case.

Thanks,
Ludo=E2=80=99.