Add (guix graph).

* guix/scripts/graph.scm (<node-type>, <graph-backend>, emit-prologue)
(emit-epilogue, emit-node, emit-edge, %graphviz-backend, export-graph):
Move to...
* guix/graph.scm: ... here.  New file.
* guix/scripts/system.scm, tests/graph.scm: Use it.
* Makefile.am (MODULES): Add it.

5 files changed, 136 insertions, 99 deletions

diff --git a/Makefile.am b/Makefile.am
index 67d483bfb0..43be2ec89e 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -50,6 +50,7 @@ MODULES =					\
   guix/gnu-maintenance.scm			\
   guix/upstream.scm				\
   guix/licenses.scm				\
+  guix/graph.scm				\
   guix/build-system.scm				\
   guix/build-system/cmake.scm			\
   guix/build-system/emacs.scm			\
diff --git a/guix/graph.scm b/guix/graph.scm
new file mode 100644
index 0000000000..05325ba0a6
--- /dev/null
+++ b/guix/graph.scm
@@ -0,0 +1,132 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2015 Ludovic Courtès <ludo@gnu.org>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (guix graph)
+  #:use-module (guix store)
+  #:use-module (guix monads)
+  #:use-module (guix records)
+  #:use-module (guix sets)
+  #:use-module (srfi srfi-9)
+  #:use-module (ice-9 match)
+  #:export (node-type
+            node-type?
+            node-type-identifier
+            node-type-label
+            node-type-edges
+            node-type-convert
+            node-type-name
+            node-type-description
+
+            %graphviz-backend
+            graph-backend?
+            graph-backend
+
+            export-graph))
+
+;;; Commentary:
+;;;
+;;; This module provides an abstract way to represent graphs and to manipulate
+;;; them.  It comes with several such representations for packages,
+;;; derivations, and store items.  It also provides a generic interface for
+;;; exporting graphs in an external format, including a Graphviz
+;;; implementation thereof.
+;;;
+;;; Code:
+
+
+;;;
+;;; Node types.
+;;;
+
+(define-record-type* <node-type> node-type make-node-type
+  node-type?
+  (identifier  node-type-identifier)              ;node -> M identifier
+  (label       node-type-label)                   ;node -> string
+  (edges       node-type-edges)                   ;node -> M list of nodes
+  (convert     node-type-convert                  ;package -> M list of nodes
+               (default (lift1 list %store-monad)))
+  (name        node-type-name)                    ;string
+  (description node-type-description))            ;string
+
+
+;;;
+;;; Graphviz export.
+;;;
+
+(define-record-type <graph-backend>
+  (graph-backend prologue epilogue node edge)
+  graph-backend?
+  (prologue graph-backend-prologue)
+  (epilogue graph-backend-epilogue)
+  (node     graph-backend-node)
+  (edge     graph-backend-edge))
+
+(define (emit-prologue name port)
+  (format port "digraph \"Guix ~a\" {\n"
+          name))
+(define (emit-epilogue port)
+  (display "\n}\n" port))
+(define (emit-node id label port)
+  (format port "  \"~a\" [label = \"~a\", shape = box, fontname = Helvetica];~%"
+          id label))
+(define (emit-edge id1 id2 port)
+  (format port "  \"~a\" -> \"~a\" [color = red];~%"
+          id1 id2))
+
+(define %graphviz-backend
+  (graph-backend emit-prologue emit-epilogue
+                 emit-node emit-edge))
+
+(define* (export-graph sinks port
+                       #:key
+                       reverse-edges? node-type
+                       (backend %graphviz-backend))
+  "Write to PORT the representation of the DAG with the given SINKS, using the
+given BACKEND.  Use NODE-TYPE to traverse the DAG.  When REVERSE-EDGES? is
+true, draw reverse arrows."
+  (match backend
+    (($ <graph-backend> emit-prologue emit-epilogue emit-node emit-edge)
+     (emit-prologue (node-type-name node-type) port)
+
+     (match node-type
+       (($ <node-type> node-identifier node-label node-edges)
+        (let loop ((nodes   sinks)
+                   (visited (set)))
+          (match nodes
+            (()
+             (with-monad %store-monad
+               (emit-epilogue port)
+               (store-return #t)))
+            ((head . tail)
+             (mlet %store-monad ((id (node-identifier head)))
+               (if (set-contains? visited id)
+                   (loop tail visited)
+                   (mlet* %store-monad ((dependencies (node-edges head))
+                                        (ids          (mapm %store-monad
+                                                            node-identifier
+                                                            dependencies)))
+                     (emit-node id (node-label head) port)
+                     (for-each (lambda (dependency dependency-id)
+                                 (if reverse-edges?
+                                     (emit-edge dependency-id id port)
+                                     (emit-edge id dependency-id port)))
+                               dependencies ids)
+                     (loop (append dependencies tail)
+                           (set-insert id visited)))))))))))))
+
+;;; graph.scm ends here
diff --git a/guix/scripts/graph.scm b/guix/scripts/graph.scm
index 734a47719a..f607ebee31 100644
--- a/guix/scripts/graph.scm
+++ b/guix/scripts/graph.scm
@@ -18,6 +18,7 @@
 
 (define-module (guix scripts graph)
   #:use-module (guix ui)
+  #:use-module (guix graph)
   #:use-module (guix scripts)
   #:use-module (guix utils)
   #:use-module (guix packages)
@@ -28,9 +29,7 @@
   #:use-module ((guix build-system gnu) #:select (standard-packages))
   #:use-module (gnu packages)
   #:use-module (guix sets)
-  #:use-module (guix records)
   #:use-module (srfi srfi-1)
-  #:use-module (srfi srfi-9)
   #:use-module (srfi srfi-34)
   #:use-module (srfi srfi-37)
   #:use-module (ice-9 match)
@@ -41,40 +40,10 @@
             %reference-node-type
             %node-types
 
-            node-type
-            node-type?
-            node-type-identifier
-            node-type-label
-            node-type-edges
-            node-type-convert
-            node-type-name
-            node-type-description
-
-            %graphviz-backend
-            graph-backend?
-            graph-backend
-
-            export-graph
-
             guix-graph))
 
 
 ;;;
-;;; Node types.
-;;;
-
-(define-record-type* <node-type> node-type make-node-type
-  node-type?
-  (identifier  node-type-identifier)              ;node -> M identifier
-  (label       node-type-label)                   ;node -> string
-  (edges       node-type-edges)                   ;node -> M list of nodes
-  (convert     node-type-convert                  ;package -> M list of nodes
-               (default (lift1 list %store-monad)))
-  (name        node-type-name)                    ;string
-  (description node-type-description))            ;string
-
-
-;;;
 ;;; Package DAG.
 ;;;
 
@@ -293,73 +262,6 @@ substitutes."
 
 
 ;;;
-;;; Graphviz export.
-;;;
-
-(define-record-type <graph-backend>
-  (graph-backend prologue epilogue node edge)
-  graph-backend?
-  (prologue graph-backend-prologue)
-  (epilogue graph-backend-epilogue)
-  (node     graph-backend-node)
-  (edge     graph-backend-edge))
-
-(define (emit-prologue name port)
-  (format port "digraph \"Guix ~a\" {\n"
-          name))
-(define (emit-epilogue port)
-  (display "\n}\n" port))
-(define (emit-node id label port)
-  (format port "  \"~a\" [label = \"~a\", shape = box, fontname = Helvetica];~%"
-          id label))
-(define (emit-edge id1 id2 port)
-  (format port "  \"~a\" -> \"~a\" [color = red];~%"
-          id1 id2))
-
-(define %graphviz-backend
-  (graph-backend emit-prologue emit-epilogue
-                 emit-node emit-edge))
-
-(define* (export-graph sinks port
-                       #:key
-                       reverse-edges?
-                       (node-type %package-node-type)
-                       (backend %graphviz-backend))
-  "Write to PORT the representation of the DAG with the given SINKS, using the
-given BACKEND.  Use NODE-TYPE to traverse the DAG.  When REVERSE-EDGES? is
-true, draw reverse arrows."
-  (match backend
-    (($ <graph-backend> emit-prologue emit-epilogue emit-node emit-edge)
-     (emit-prologue (node-type-name node-type) port)
-
-     (match node-type
-       (($ <node-type> node-identifier node-label node-edges)
-        (let loop ((nodes   sinks)
-                   (visited (set)))
-          (match nodes
-            (()
-             (with-monad %store-monad
-               (emit-epilogue port)
-               (store-return #t)))
-            ((head . tail)
-             (mlet %store-monad ((id (node-identifier head)))
-               (if (set-contains? visited id)
-                   (loop tail visited)
-                   (mlet* %store-monad ((dependencies (node-edges head))
-                                        (ids          (mapm %store-monad
-                                                            node-identifier
-                                                            dependencies)))
-                     (emit-node id (node-label head) port)
-                     (for-each (lambda (dependency dependency-id)
-                                 (if reverse-edges?
-                                     (emit-edge dependency-id id port)
-                                     (emit-edge id dependency-id port)))
-                               dependencies ids)
-                     (loop (append dependencies tail)
-                           (set-insert id visited)))))))))))))
-
-
-;;;
 ;;; Command-line options.
 ;;;
 
diff --git a/guix/scripts/system.scm b/guix/scripts/system.scm
index 0d54d453db..1407dc73fa 100644
--- a/guix/scripts/system.scm
+++ b/guix/scripts/system.scm
@@ -29,6 +29,7 @@
   #:use-module (guix profiles)
   #:use-module (guix scripts)
   #:use-module (guix scripts build)
+  #:use-module (guix graph)
   #:use-module (guix scripts graph)
   #:use-module (guix build utils)
   #:use-module (gnu build install)
diff --git a/tests/graph.scm b/tests/graph.scm
index f454b06351..ed5849f4da 100644
--- a/tests/graph.scm
+++ b/tests/graph.scm
@@ -18,6 +18,7 @@
 
 (define-module (test-graph)
   #:use-module (guix tests)
+  #:use-module (guix graph)
   #:use-module (guix scripts graph)
   #:use-module (guix packages)
   #:use-module (guix derivations)