From c8c25704aeb2e5fa4feb6a86235f9565738eea99 Mon Sep 17 00:00:00 2001
From: Ludovic Courtès <ludo@gnu.org>
Date: Tue, 6 Sep 2016 20:19:21 +0200
Subject: profiles: Add manifest-transaction helper procedures.

* guix/profiles.scm (manifest-transaction-install-entry)
(manifest-transaction-remove-pattern)
(manifest-transaction-null?): New procedures.
* tests/profiles.scm ("manifest-transaction-null?"): New test.
---
 guix/profiles.scm | 27 ++++++++++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)

(limited to 'guix/profiles.scm')

diff --git a/guix/profiles.scm b/guix/profiles.scm
index cd448e3f25..ac2fa051b2 100644
--- a/guix/profiles.scm
+++ b/guix/profiles.scm
@@ -78,6 +78,9 @@ (define-module (guix profiles)
             manifest-transaction?
             manifest-transaction-install
             manifest-transaction-remove
+            manifest-transaction-install-entry
+            manifest-transaction-remove-pattern
+            manifest-transaction-null?
             manifest-perform-transaction
             manifest-transaction-effects
 
@@ -383,6 +386,28 @@ (define-record-type* <manifest-transaction> manifest-transaction
   (remove  manifest-transaction-remove  ; list of <manifest-pattern>
            (default '())))
 
+(define (manifest-transaction-install-entry entry transaction)
+  "Augment TRANSACTION's set of installed packages with ENTRY, a
+<manifest-entry>."
+  (manifest-transaction
+   (inherit transaction)
+   (install
+    (cons entry (manifest-transaction-install transaction)))))
+
+(define (manifest-transaction-remove-pattern pattern transaction)
+  "Add PATTERN to TRANSACTION's list of packages to remove."
+  (manifest-transaction
+   (inherit transaction)
+   (remove
+    (cons pattern (manifest-transaction-remove transaction)))))
+
+(define (manifest-transaction-null? transaction)
+  "Return true if TRANSACTION has no effect---i.e., it neither installs nor
+remove software."
+  (match transaction
+    (($ <manifest-transaction> () ()) #t)
+    (($ <manifest-transaction> _ _)   #f)))
+
 (define (manifest-transaction-effects manifest transaction)
   "Compute the effect of applying TRANSACTION to MANIFEST.  Return 4 values:
 the list of packages that would be removed, installed, upgraded, or downgraded
@@ -424,7 +449,7 @@ (define (manifest-entry->pattern entry)
                    downgrade)))))))
 
 (define (manifest-perform-transaction manifest transaction)
-  "Perform TRANSACTION on MANIFEST and return new manifest."
+  "Perform TRANSACTION on MANIFEST and return the new manifest."
   (let ((install (manifest-transaction-install transaction))
         (remove  (manifest-transaction-remove transaction)))
     (manifest-add (manifest-remove manifest remove)
-- 
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