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/*
* Copyright (C) 2007-2008, Jeff Thompson
*
* 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 the copyright holder 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.
*/
using System;
using System.Collections.Generic;
using System.Text;
namespace OpenSim.Region.ScriptEngine.Shared.YieldProlog
{
public class Atom : IUnifiable
{
private static Dictionary<string, Atom> _atomStore = new Dictionary<string, Atom>();
public readonly string _name;
public readonly Atom _module;
/// <summary>
/// You should not call this constructor, but use Atom.a instead.
/// </summary>
/// <param name="name"></param>
/// <param name="module"></param>
private Atom(string name, Atom module)
{
_name = name;
_module = module;
}
/// <summary>
/// Return the unique Atom object for name where module is null. You should use this to create
/// an Atom instead of calling the Atom constructor.
/// </summary>
/// <param name="name"></param>
/// <returns></returns>
public static Atom a(string name)
{
Atom atom;
if (!_atomStore.TryGetValue(name, out atom))
{
atom = new Atom(name, null);
_atomStore[name] = atom;
}
return atom;
}
/// <summary>
/// Return an Atom object with the name and module. If module is null or Atom.NIL,
/// this behaves like Atom.a(name) and returns the unique object where the module is null.
/// If module is not null or Atom.NIL, this may or may not be the same object as another Atom
/// with the same name and module.
/// </summary>
/// <param name="name"></param>
/// <param name="module"></param>
/// <returns></returns>
public static Atom a(string name, Atom module)
{
if (module == null || module == Atom.NIL)
return a(name);
return new Atom(name, module);
}
/// <summary>
/// If Obj is an Atom unify its _module with Module. If the Atom's _module is null, use Atom.NIL.
/// </summary>
/// <param name="Atom"></param>
/// <param name="Module"></param>
/// <returns></returns>
public static IEnumerable<bool> module(object Obj, object Module)
{
Obj = YP.getValue(Obj);
if (Obj is Atom)
{
if (((Atom)Obj)._module == null)
return YP.unify(Module, Atom.NIL);
else
return YP.unify(Module, ((Atom)Obj)._module);
}
return YP.fail();
}
public static readonly Atom NIL = Atom.a("[]");
public static readonly Atom DOT = Atom.a(".");
public static readonly Atom F = Atom.a("f");
public static readonly Atom SLASH = Atom.a("/");
public static readonly Atom HAT = Atom.a("^");
public static readonly Atom RULE = Atom.a(":-");
public IEnumerable<bool> unify(object arg)
{
arg = YP.getValue(arg);
if (arg is Atom)
return Equals(arg) ? YP.succeed() : YP.fail();
else if (arg is Variable)
return ((Variable)arg).unify(this);
else
return YP.fail();
}
public void addUniqueVariables(List<Variable> variableSet)
{
// Atom does not contain variables.
}
public object makeCopy(Variable.CopyStore copyStore)
{
// Atom does not contain variables that need to be copied.
return this;
}
public bool termEqual(object term)
{
return Equals(YP.getValue(term));
}
public bool ground()
{
// Atom is always ground.
return true;
}
public override bool Equals(object obj)
{
if (obj is Atom)
{
if (_module == null && ((Atom)obj)._module == null)
// When _declaringClass is null, we always use an identical object from _atomStore.
return this == obj;
// Otherwise, ignore _declaringClass and do a normal string compare on the _name.
return _name == ((Atom)obj)._name;
}
return false;
}
public override string ToString()
{
return _name;
}
public override int GetHashCode()
{
// Debug: need to check _declaringClass.
return _name.GetHashCode();
}
public string toQuotedString()
{
if (_name.Length == 0)
return "''";
else if (this == Atom.NIL)
return "[]";
StringBuilder result = new StringBuilder(_name.Length);
bool useQuotes = false;
foreach (char c in _name)
{
int cInt = (int)c;
if (c == '\'')
{
result.Append("''");
useQuotes = true;
}
else if (c == '_' || cInt >= (int)'a' && cInt <= (int)'z' ||
cInt >= (int)'A' && cInt <= (int)'Z' || cInt >= (int)'0' && cInt <= (int)'9')
result.Append(c);
else
{
// Debug: Need to handle non-printable chars.
result.Append(c);
useQuotes = true;
}
}
if (!useQuotes && (int)_name[0] >= (int)'a' && (int)_name[0] <= (int)'z')
return result.ToString();
else
{
// Surround in single quotes.
result.Append('\'');
return "'" + result;
}
}
/// <summary>
/// Return true if _name is lexicographically less than atom._name.
/// </summary>
/// <param name="atom"></param>
/// <returns></returns>
public bool lessThan(Atom atom)
{
return _name.CompareTo(atom._name) < 0;
}
}
}
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