From cb53d087b23da10259d9ecb9faf2a221956b0b07 Mon Sep 17 00:00:00 2001
From: Costa Vitor <vitor@eagle.biostat.wisc.edu>
Date: Fri, 24 Aug 2012 15:19:15 -0500
Subject: [PATCH] add rb_fold/4.

---
 docs/yap.tex        | 11 +++++++++++
 library/rbtrees.yap | 26 ++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/docs/yap.tex b/docs/yap.tex
index 377050407..fb8847c55 100644
--- a/docs/yap.tex
+++ b/docs/yap.tex
@@ -10910,6 +10910,17 @@ holds, then the value associated with @var{Key} in @var{TN} is
 @var{ValF}. Fails if or if @code{call(G,Val0,ValF)} is not satisfiable
 for all @var{Var0}. Assumes keys are not repeated.
 
+@item rb_fold(+@var{T},+@var{G},+@var{Acc0}, -@var{AccF})
+@findex rb_fold/4
+@snindex rb_fold/4
+@cnindex rb_fold/4
+	For all nodes @var{Key} in the tree @var{T}, if the value
+associated with key @var{Key} is @var{V} in tree @var{T}, if
+@code{call(G,V,Acc1,Acc2)} holds, then if @var{VL} is value of the
+previous node in inorder, @code{call(G,VL,_,Acc0)} must hold, and if
+@var{VR} is the value of the next node in inorder,
+@code{call(G,VR,Acc1,_)} must hold.
+
 @item rb_clone(+@var{T},+@var{NT},+@var{Nodes})
 @findex rb_clone/3
 @snindex rb_clone/3
diff --git a/library/rbtrees.yap b/library/rbtrees.yap
index 9bb606046..aa1734cb3 100644
--- a/library/rbtrees.yap
+++ b/library/rbtrees.yap
@@ -30,6 +30,7 @@
 	   rb_map/2,
 	   rb_map/3,
 	   rb_partial_map/4,
+	   rb_accumulate/4,
 	   rb_clone/3,
 	   rb_clone/4,
 	   rb_min/3,
@@ -820,6 +821,31 @@ map(black(L,_,V,R),Goal) :-
 	map(L,Goal),
 	map(R,Goal).
 
+:- meta_predicate rb_accumulate(?,3,?,?).  % this is required.
+:- meta_predicate map_acc(?,3,?,?).  % this is required.
+
+%%	rb_fold(+T, :G, +Acc0, -AccF) is semidet.
+%
+%	For all nodes Key in the tree   T,  if the value associated with
+%	key Key is V in tree T, if call(G,V,Acc1,Acc2) holds, then
+%	if VL is value of the previous node in inorder,
+%       call(G,VL,_,Acc0) must hold, and
+%       if VR is the value of the next node in inorder,
+%       call(G,VR,Acc1,_) must hold.
+
+rb_fold(t(_,Tree), Goal, In, Out) :-
+	map_acc(Tree, Goal, In, Out).
+
+map_acc(black('',_,_,''), _, Acc, Acc) :- !.
+map_acc(red(L,_,V,R), Goal, Left, Right) :-
+	map_acc(L,Goal, Left, Left1),
+	once(call(Goal,V, Left1, Right1)),
+	map_acc(R,Goal, Right1, Right).
+map_acc(black(L,_,V,R), Goal, Left, Right) :-
+	map_acc(L,Goal, Left, Left1),
+	once(call(Goal,V, Left1, Right1)),
+	map_acc(R,Goal, Right1, Right).
+
 %%	rb_clone(+T, -NT, -Pairs)
 %
 %	"Clone" the red-back tree into a new  tree with the same keys as