Christopher Baines <mail@cbaines.net> skribis:

> Add a more flexible variant of the fold-packages procedure, that takes a list
> of the modules to work with. The existing fold-packages procedure then calls
> fold-packages-in-modules with the result of the all-modules procedure.
>
> I wrote this when looking at how to get the packages in a specific set of
> modules, to create jobs for cuirass.
>
> * gnu/packages.scm (fold-packages-in-modules): New procedure.
>   (fold-packages): Change to use fold-packages-in-modules.

[...]

> +(define (fold-packages-in-modules modules proc init)
> +  "Call (PROC PACKAGE RESULT) for each available package within any of the
> +modules in MODULES, using INIT as the initial value of RESULT.  It is
> +guaranteed to never traverse the same package twice."
>    (fold-module-public-variables (lambda (object result)
>                                    (if (and (package? object)
>                                             (not (hidden-package? object)))
>                                        (proc object result)
>                                        result))
>                                  init
> -                                (all-modules (%package-module-path))))
> +                                modules))

Instead of introducing a new procedure, what about simply: