/YieldProlog/Modules/ListPair.cs

/*

 * Copyright (c) Contributors, http://aurora-sim.org/

 * See CONTRIBUTORS.TXT for a full list of copyright holders.

 *

 * 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 the Aurora-Sim Project 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 DEVELOPERS ``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 CONTRIBUTORS BE LIABLE FOR ANY

 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES

 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;

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 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 */



using System;

using System.Collections.Generic;



namespace OpenSim.Region.ScriptEngine.Shared.YieldProlog

{

    public class ListPair : Functor2

    {

        public ListPair(object head, object tail) : base(Atom.DOT, head, tail)

        {

        }



        public static object make(List<object> list)

        {

            if (list.Count <= 0)

                return Atom.NIL;



            object result = Atom.NIL;

            // Start from the end.

            for (int i = list.Count - 1; i >= 0; --i)

                result = new ListPair(list[i], result);

            return result;

        }



        public static object make(object[] array)

        {

            if (array.Length <= 0)

                return Atom.NIL;



            object result = Atom.NIL;

            // Start from the end.

            for (int i = array.Length - 1; i >= 0; --i)

                result = new ListPair(array[i], result);

            return result;

        }



        /// <summary>

        /// Return a ListPair version of array, where repeated elements

        /// (according to YP.termEqual) are removed.

        /// </summary>

        /// <param name="array"></param>

        /// <returns></returns>

        public static object makeWithoutRepeatedTerms(object[] array)

        {

            if (array.Length <= 0)

                return Atom.NIL;



            // Start from the end.

            object previousTerm = array[array.Length - 1];

            object result = new ListPair(previousTerm, Atom.NIL);

            for (int i = array.Length - 2; i >= 0; --i)

            {

                object term = array[i];

                if (YP.termEqual(term, previousTerm))

                    continue;

                result = new ListPair(term, result);

                previousTerm = term;

            }

            return result;

        }



        /// <summary>

        /// Return a ListPair version of array, where repeated elements

        /// (according to YP.termEqual) are removed.

        /// </summary>

        /// <param name="array"></param>

        /// <returns></returns>

        public static object makeWithoutRepeatedTerms(List<object> array)

        {

            if (array.Count <= 0)

                return Atom.NIL;



            // Start from the end.

            object previousTerm = array[array.Count - 1];

            object result = new ListPair(previousTerm, Atom.NIL);

            for (int i = array.Count - 2; i >= 0; --i)

            {

                object term = array[i];

                if (YP.termEqual(term, previousTerm))

                    continue;

                result = new ListPair(term, result);

                previousTerm = term;

            }

            return result;

        }



        public static object make(object element1)

        {

            return new ListPair(element1, Atom.NIL);

        }



        public static object make(object element1, object element2)

        {

            return new ListPair(element1, new ListPair(element2, Atom.NIL));

        }



        public static object make(object element1, object element2, object element3)

        {

            return new ListPair(element1,

                new ListPair(element2, new ListPair(element3, Atom.NIL)));

        }



        /// <summary>

        /// Return an array of the elements in list or null if it is not

        /// a proper list.  If list is Atom.NIL, return an array of zero elements.

        /// If the list or one of the tails of the list is Variable, raise an instantiation_error.

        /// This does not call YP.getValue on each element.

        /// </summary>

        /// <param name="list"></param>

        /// <returns></returns>

        public static object[] toArray(object list)

        {

            list = YP.getValue(list);

            if (list.Equals(Atom.NIL))

                return new object[0];



            List<object> result = new List<object>();

            object element = list;

            while (true) {

                if (element == Atom.NIL)

                    break;

                if (element is Variable)

                    throw new PrologException(Atom.a("instantiation_error"),

                        "List tail is an unbound variable");

                if (!(element is Functor2 && ((Functor2)element)._name == Atom.DOT))

                    // Not a proper list.

                    return null;

                result.Add(((Functor2)element)._arg1);

                element = YP.getValue(((Functor2)element)._arg2);

            }



            if (result.Count <= 0)

                return null;

            return result.ToArray();

        }

    }

}