From a599699f0ce9e9dadd15d8e169f66b7ab0bf6132 Mon Sep 17 00:00:00 2001
From: Vitor Santos Costa <vsc@dcc.fc.up.pt>
Date: Sun, 24 Mar 2013 09:12:55 -0500
Subject: [PATCH] new dgraph path predicate

---
 docs/yap.tex        |  7 +++++++
 library/dgraphs.yap | 28 +++++++++++++++++++++++-----
 2 files changed, 30 insertions(+), 5 deletions(-)

diff --git a/docs/yap.tex b/docs/yap.tex
index 03a46c57c..c05fbf3da 100644
--- a/docs/yap.tex
+++ b/docs/yap.tex
@@ -12840,6 +12840,13 @@ vertices in @var{Vs} map to vertices in @var{NewVs}.
 The path @var{Path} is a path starting at vertex @var{Vertex} in graph
 @var{Graph}.
 
+@item dgraph_path(+@var{Vertex}, +@var{Vertex1}, +@var{Graph}, ?@var{Path})
+@findex  dgraph_path/3
+@snindex dgraph_path/3
+@cnindex dgraph_path/3
+The path @var{Path} is a path starting at vertex @var{Vertex} in graph
+@var{Graph} and ending at path @var{Vertex2}.
+
 @item dgraph_reachable(+@var{Vertex}, +@var{Graph}, ?@var{Edges})
 @findex  dgraph_path/3
 @snindex dgraph_path/3
diff --git a/library/dgraphs.yap b/library/dgraphs.yap
index e081bc3bd..f75b79ac1 100644
--- a/library/dgraphs.yap
+++ b/library/dgraphs.yap
@@ -32,6 +32,7 @@
 	    dgraph_min_paths/3,
 	    dgraph_isomorphic/4,
 	    dgraph_path/3,
+	    dgraph_path/4,
 	    dgraph_leaves/2,
 	    dgraph_reachable/3
 	]).
@@ -40,7 +41,8 @@
 	[rb_new/1 as dgraph_new]).
 
 :- use_module(library(rbtrees),
-	[rb_empty/1,
+	[rb_new/1,
+	 rb_empty/1,
 	 rb_lookup/3,
 	 rb_apply/4,
 	 rb_insert/4,
@@ -361,10 +363,21 @@ dgraph_min_paths(V1, Graph, Paths) :-
 	dgraph_to_wdgraph(Graph, WGraph),
 	wdgraph_min_paths(V1, WGraph, Paths).
 
-dgraph_path(V, G, [V|P]) :-
-	rb_lookup(V, Children, G),
-	ord_del_element(Children, V, Ch),
-	do_path(Ch, G, [V], P).
+dgraph_path(V1, V2, Graph, Path) :-
+	rb_new(E0),
+	rb_lookup(V1, Children, Graph),
+	dgraph_path_children(Children, V2, E0, Graph, Path).
+
+dgraph_path_children([V1|_], V2, _E1, _Graph, []) :- V1 == V2.
+dgraph_path_children([V1|_], V2, E1, Graph, [V1|Path]) :-
+	V2 \== V1,
+	\+ rb_lookup(V1, _, E0),
+	rb_insert(E0, V2, [], E1),
+	rb_lookup(V1, Children, Graph),
+	dgraph_path_children(Children, V2, E1, Graph, Path).
+dgraph_path_children([_|Children], V2, E1, Graph, Path) :-
+	dgraph_path_children(Children, V2, E1, Graph, Path).
+
 
 do_path([], _, _, []).
 do_path([C|Children], G, SoFar, Path) :-
@@ -378,6 +391,11 @@ do_children([V|_], G, SoFar, [V|Path]) :-
 do_children([_|Children], G, SoFar, Path) :-
 	do_children(Children, G, SoFar, Path).
 
+dgraph_path(V, G, [V|P]) :-
+	rb_lookup(V, Children, G),
+	ord_del_element(Children, V, Ch),
+	do_path(Ch, G, [V], P).
+
 
 dgraph_isomorphic(Vs, Vs2, G1, G2) :-
 	rb_new(Map0),