content: /*******************************************************************************
  * Copyright (c) 2010-2011 Luaj.org. All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
  * in the Software without restriction, including without limitation the rights
  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  * copies of the Software, and to permit persons to whom the Software is
  * furnished to do so, subject to the following conditions:
  *
  * The above copyright notice and this permission notice shall be included in
  * all copies or substantial portions of the Software.
  * 
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  ******************************************************************************/
  package org.luaj.vm2;
  
  import org.luaj.vm2.Varargs.ArrayPartVarargs;
  import org.luaj.vm2.Varargs.PairVarargs;
  
  /**
   * Subclass of {@link Varargs} that represents a lua tail call 
   * in a Java library function execution environment. 
   * <p>
   * Since Java doesn't have direct support for tail calls, 
   * any lua function whose {@link Prototype} contains the 
   * {@link Lua#OP_TAILCALL} bytecode needs a mechanism 
   * for tail calls when converting lua-bytecode to java-bytecode.
   * <p>
   * The tail call holds the next function and arguments, 
   * and the client a call to {@link #eval()} executes the function
   * repeatedly until the tail calls are completed. 
   * <p>
   * Normally, users of luaj need not concern themselves with the 
   * details of this mechanism, as it is built into the core 
   * execution framework. 
   * @see Prototype 
   * @see LuaJC
   */
  public class TailcallVarargs extends Varargs {
  
  	private LuaValue func;
  	private Varargs args;
  	private Varargs result;
  	
  	public TailcallVarargs(LuaValue f, Varargs args) {
  		this.func = f;
  		this.args = args;
  	}
  	
  	public TailcallVarargs(LuaValue object, LuaValue methodname, Varargs args) {
  		this.func = object.get(methodname);
  		this.args = LuaValue.varargsOf(object, args);
  	}
  	
  	public boolean isTailcall() {
  		return true;
  	}
  	
  	public Varargs eval() {
  		while ( result == null ) {
  			Varargs r = func.onInvoke(args);
  			if (r.isTailcall()) {
  				TailcallVarargs t = (TailcallVarargs) r;
  				func = t.func;
  				args = t.args;
  			}
  			else {
  				result = r;			
  				func = null;
  				args = null;
  			}
  		}
  		return result;
  	}
  	
  	public LuaValue arg( int i ) {
  		if ( result == null )
  			eval();
  		return result.arg(i);
  	}
  	
  	public LuaValue arg1() {
  		if (result == null)
  			eval();
  		return result.arg1();
  	}
  	
  	public int narg() {
  		if (result == null)
  			eval();
  		return result.narg();
  	}
  
  	public Varargs subargs(int start) {
  		if (result == null)
  			eval();
  		return result.subargs(start);
  	}
  }