Subject: Re: [bug#28274] [PATCH] gnu: Add fold-packages-in-modules.

From: [email-masked] (Ludovic Courtès)
Date: Thu, 31 Aug 2017 15:20:55 +0200

Christopher Baines <[email-masked]> 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:

diff --git a/gnu/packages.scm b/gnu/packages.scm
index 562906178..b4ac6661c 100644
--- a/gnu/packages.scm
+++ b/gnu/packages.scm
@@ -140,17 +140,19 @@ for system '~a'")
               directory))
         %load-path)))
 
-(define (fold-packages proc init)
-  "Call (PROC PACKAGE RESULT) for each available package, using INIT as
-the initial value of RESULT.  It is guaranteed to never traverse the
-same package twice."
+(define* (fold-packages proc init
+                        #:optional
+                        (modules (all-modules (%package-module-path))))
+  "Call (PROC PACKAGE RESULT) for each available package defined in one of
+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))
 
 (define find-packages-by-name
   (let ((packages (delay

?

Ludo’.