Ludovic Courtès (2016-05-08 21:40 +0300) wrote:

> Alex Kost <alezost@gmail.com> skribis:
>
>> * emacs/guix-main.scm (register-package, packages-from-file): New procedures.
>> (%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/

Fixed.

>> +(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 ‘table’ a promise…

I don't like this 'table*' procedure (especially its name), and I would
like to get rid of it, but I couldn't make your suggestion work…

>> +    (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*)))))))
>
> … by wrapping ‘vhash-consq’ in ‘delay’.

… I tried it, but I got an error I don't know what to do with:

  Throw to key `vm-error' with args `(vm-run "VM: Stack overflow" ())'.

I attach the file that illustrates this problem.  Here is the recipe to
reproduce it using geiser:

1. M-x run-guile
2. Open the attached file
3. Evaluate it: C-c C-b

And the last expression leads to an error (at least for me).  Is there
some problem with combining force/delay or did I do something wrong?

> To avoid ‘set!’ 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’t need to
>      remember the package.

I don't like this solution.  With "M-x guix-package-from-file" you get a
full-featured *Guix Package Info* buffer, where you can not only install
the package, but download its source, look at its license, inputs,
etc. (and soon it will be possible just to build it without installing).

>   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.

Ouch, this looks scary to me, so I stay on the current solution, but
thanks for the pointers!