[PATCH] gnu: add emacs-undo-tree

[KAction]

From: Dmitry Bogatov <address@hidden>

  * gnu/packages/emacs.scm (emacs-undo-tree): New variable
---
 gnu/packages/emacs.scm | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/gnu/packages/emacs.scm b/gnu/packages/emacs.scm
index 7d95f55..2fd39a3 100644
--- a/gnu/packages/emacs.scm
+++ b/gnu/packages/emacs.scm
@@ -1007,6 +1007,42 @@ and stored in memory.")
     (description "This package provides a modern list API library for Emacs.")
     (license license:gpl3+)))
 
+;; Version in source is 0.6.6, but both source repository
+;; and web-site , pkgnamerefers to 0.6.4.
+(define-public emacs-undo-tree
+  (package
+    (name "emacs-undo-tree")
+    (version "0.6.4")
+    (source (origin
+              (method git-fetch)
+              (uri (git-reference
+                    (url "http://dr-qubit.org/git/undo-tree.git";)
+                    (commit "release/0.6.4")))
+              (sha256
+                (base32
+                  "0b6hnv6bq1g5np5q2yw9r9aj1cxpp14akm21br7vpb7wp01fv4b3"))))
+    (build-system emacs-build-system)
+    (home-page "http://www.dr-qubit.org/emacs.php";)
+    (synopsis "Treat undo history as a tree")
+
+    (description "Emacs has a powerful undo system. Unlike the standard
+undo/redo system in most software, it allows you to recover *any* past state
+of a buffer (whereas the standard undo/redo system can lose past states as
+soon as you redo). However, this power comes at a price: many people find 
Emacs'
+undo system confusing and difficult to use, spawning a number of packages that
+replace it with the less powerful but more intuitive undo/redo system.
+
+Both the loss of data with standard undo/redo, and the confusion of Emacs'
+undo, stem from trying to treat undo history as a linear sequence of changes.
+It's not. The `undo-tree-mode' provided by this package replaces Emacs' undo
+system with a system that treats undo history as what it is: a branching tree
+of changes. This simple idea allows the more intuitive behaviour of the
+standard undo/redo system to be combined with the power of never losing any
+history. An added side bonus is that undo history can in some cases be stored
+more efficiently, allowing more changes to accumulate before Emacs starts
+discarding history.")
+    (license license:gpl3+)))
+
 (define-public emacs-s
   (package
     (name "emacs-s")
-- 
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