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

[Christopher Baines <mail@cbaines.net>]

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.
---
 gnu/packages.scm | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/gnu/packages.scm b/gnu/packages.scm
index 562906178..3f0ff56b8 100644
--- a/gnu/packages.scm
+++ b/gnu/packages.scm
@@ -47,6 +47,7 @@
             %bootstrap-binaries-path
             %package-module-path
 
+            fold-packages-in-modules
             fold-packages
 
             find-packages-by-name
@@ -144,13 +145,21 @@ for system '~a'")
   "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."
+  (fold-packages-in-modules (all-modules (%package-module-path))
+                            proc
+                            init))
+
+(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))
 
 (define find-packages-by-name
   (let ((packages (delay
-- 
2.14.1