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diff --git a/gee/unfolditerator.vala b/gee/unfolditerator.vala
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+/* unfolditerator.vala
+ *
+ * Copyright (C) 2011  Maciej Piechotka
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+
+ * This library 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
+ * Lesser General Public License for more details.
+
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301  USA
+ *
+ * Author:
+ * 	Maciej Piechotka <uzytkownik2@gmail.com>
+ */
+
+internal class Gee.UnfoldIterator<G> : Object, Traversable<G>, Iterator<G> {
+	public UnfoldIterator (owned UnfoldFunc<G> func, owned Lazy<G>? current = null) {
+		_current = (owned)current;
+		_func = (owned)func;
+		_end = false;
+	}
+
+	public bool next () {
+		if (has_next ()) {
+			if (_current != null)
+				_current.eval ();
+			_current = (owned)_next;
+			return true;
+		}
+		return false;
+	}
+
+	public bool has_next () {
+		if (_end)
+			return false;
+		if (_next != null)
+			return true;
+		_next = _func ();
+		if (_next == null)
+			_end = true;
+		return _next != null;
+	}
+
+	public new G get () {
+		assert (_current != null);
+		return _current.value;
+	}
+
+	public void remove () {
+		assert_not_reached ();
+	}
+
+	public bool valid { get { return _current != null; } }
+	public bool read_only { get { return true; } }
+
+	public bool foreach (ForallFunc<G> f) {
+		if (_current != null) {
+			if (!f (_current)) {
+				return false;
+			}
+		}
+		if (_next != null) {
+			_current = (owned)_next;
+			if (!f (_current)) {
+				return false;
+			}
+		} else if (_end) {
+			return true;
+		}
+		if (_current == null) {
+			_current = _func ();
+			if (_current == null) {
+				_end = true;
+				return true;
+			} else {
+				if (!f (_current)) {
+					return false;
+				}
+			}
+		}
+		while ((_next = _func ()) != null) {
+			_current = (owned)_next;
+			if (!f (_current)) {
+				return false;
+			}
+		}
+		_end = true;
+		return true;
+	}
+
+	private UnfoldFunc<G> _func;
+	private Lazy<G>? _current;
+	private Lazy<G>? _next;
+	private bool _end;
+}