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+/*
+ * Copyright (c) 2003-2009, John Wiegley.  All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ *   notice, this list of conditions and the following disclaimer in the
+ *   documentation and/or other materials provided with the distribution.
+ *
+ * - Neither the name of New Artisans LLC nor the names of its
+ *   contributors may be used to endorse or promote products derived from
+ *   this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/**
+ * @addtogroup data
+ */
+
+/**
+ * @file   compare.h
+ * @author John Wiegley
+ *
+ * @ingroup data
+ */
+#ifndef _COMPARE_H
+#define _COMPARE_H
+
+#include "expr.h"
+
+namespace ledger {
+
+class post_t;
+class account_t;
+
+void push_sort_value(std::list<sort_value_t>& sort_values,
+		     expr_t::ptr_op_t node, scope_t& scope);
+
+template <typename T>
+class compare_items
+{
+  expr_t sort_order;
+
+  compare_items();
+  
+public:
+  compare_items(const compare_items& other) : sort_order(other.sort_order) {
+    TRACE_CTOR(compare_items, "copy");
+  }
+  compare_items(const expr_t& _sort_order) : sort_order(_sort_order) {
+    TRACE_CTOR(compare_items, "const value_expr&");
+  }
+  ~compare_items() throw() {
+    TRACE_DTOR(compare_items);
+  }
+
+  void find_sort_values(std::list<sort_value_t>& sort_values, scope_t& scope) {
+    push_sort_value(sort_values, sort_order.get_op(), scope);
+  }
+
+  bool operator()(T * left, T * right);
+};
+
+sort_value_t calc_sort_value(const expr_t::ptr_op_t op);
+
+template <typename T>
+bool compare_items<T>::operator()(T * left, T * right)
+{
+  assert(left); assert(right);
+  return sort_value_is_less_than(find_sort_values(left),
+				 find_sort_values(right));
+}
+
+template <>
+bool compare_items<post_t>::operator()(post_t * left, post_t * right);
+template <>
+bool compare_items<account_t>::operator()(account_t * left,
+					  account_t * right);
+
+} // namespace ledger
+
+#endif // _COMPARE_H