Re: [PATCH 2/2] emacs: Add 'guix-package-from-file' command.

[Alex Kost]

Ludovic Courtès (2016-05-09 23:29 +0300) wrote:

> Alex Kost <address@hidden> skribis:
>
>> Ludovic Courtès (2016-05-08 21:40 +0300) wrote:
>
> [...]
>
>>> … 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 needs to be changed like this:
>
> (define-values (package-by-address
>                 register-package)
>   (let ((table (delay (fold-packages
>                        (lambda (package table)
>                          (vhash-consq (object-address package)
>                                       package table))
>                        vlist-null))))
>     (values
>      (lambda (address)
>        "Return package by its object ADDRESS."
>        (match (vhash-assq address (force table))
>          ((_ . package) package)
>          (_ #f)))
>      (lambda (package)
>        "Register PACKAGE by its 'object-address', so that later
> 'package-by-address' can be used to access it."
>        (let ((table (force table)))
>          (set! table
>            (delay (vhash-consq (object-address package)
>                                package table))))))))
>
> In the example you posted, ‘register-package’ would turn ‘table’ into a
> self-reference, hence the stack overflow.

Heh, so simple, thanks a lot!  I used this variant and committed this
patch, thanks again.

-- 
Alex