02/03: doc: Add '--manifest' example using 'specification->package+output'.

[Ludovic Courtès]

civodul pushed a commit to branch master
in repository guix.

commit 6cd1059340758669a7d98c4611f5d418b51899f2
Author: Ludovic Courtès <address@hidden>
Date:   Tue Jan 17 22:58:37 2017 +0100

    doc: Add '--manifest' example using 'specification->package+output'.
    
    * doc/guix.texi (Invoking guix package): Add --manifest example using
    'specification->package+output'.
---
 doc/guix.texi |   14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/doc/guix.texi b/doc/guix.texi
index bf9dbaa..a212666 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -1685,6 +1685,20 @@ of packages:
        (list guile-2.0 "debug")))
 @end example
 
address@hidden specification->package+output
+In this example we have to know which modules define the @code{emacs}
+and @code{guile-2.0} variables to provide the right
address@hidden line, which can be cumbersome.  We can
+instead provide regular package specifications and let
address@hidden>package-output} look up the corresponding package
+objects, like this:
+
address@hidden
+(packages->manifest
+ (map (compose list specification->package+output)
+      '("emacs" "guile@@2.0" "guile@@2.0:debug")))
address@hidden example
+
 @item --roll-back
 @cindex rolling back
 @cindex undoing transactions