flash on 2009-12-29

/**
 * Copyright foo9 ( http://wonderfl.net/user/foo9 )
 * MIT License ( http://www.opensource.org/licenses/mit-license.php )
 * Downloaded from: http://wonderfl.net/c/rmXu
 */

package
{
	import flash.display.Sprite;
	import flash.events.Event;
	import flash.text.TextField;
	import flash.text.TextFieldAutoSize;
		
	/**
	 * @see http://ja.wikipedia.org/wiki/Interpreter_%E3%83%91%E3%82%BF%E3%83%BC%E3%83%B3
	 */
	public class InterpreterPatternSample2 extends Sprite 
	{
		private static const EXPRESSION:String = "42 4 2 - +";		
		private var _parser:Parser;		
		private var _textField:TextField;
		
		public function InterpreterPatternSample2():void 
		{			
			_parser = new Parser(EXPRESSION);
			
			_textField = new TextField();
			addChild(_textField);
			_textField.autoSize = TextFieldAutoSize.LEFT;
			_textField.text = "\'" + EXPRESSION + "\'" + " equals " + _parser.evaluate();
		}		
	}
}


interface IExpression 
{
	function interpret(s:Vector.<Number>):void;
}
	

class NumberExpression implements IExpression
{
	private var _number:Number;
	
	public function NumberExpression(number:Number) 
	{	
		_number = number;
	}
	
	public function interpret(s:Vector.<Number>):void
	{		
		s.push(_number);			
	}
}	


class PlusExpression implements IExpression
{
	
	public function PlusExpression() 
	{			
	}
	
	public function interpret(s:Vector.<Number>):void
	{		
		s.push(s.pop() + s.pop());
	}
}	


class MinusExpression implements IExpression
{
	
	public function MinusExpression() 
	{
	}
	
	public function interpret(s:Vector.<Number>):void
	{
		s.push(-s.pop() + s.pop());			
	}
}	


class Parser 
{
	private var _parseTree:Vector.<IExpression> = new Vector.<IExpression>();
	
	public function Parser(s:String) 
	{
		var arr:Array = s.split(" "); 
		for each (var token:String in arr)
		{				
			switch(token)
			{
				case "+":
					_parseTree.push(new PlusExpression());
					break;					
				case "-":
					_parseTree.push(new MinusExpression());
					break;					
				default:						
					_parseTree.push(new NumberExpression(Number(token)));
			}
		}
	}
	
	public function evaluate():int
	{
		var _context:Vector.<Number> = new Vector.<Number>();
		for each(var e:IExpression in _parseTree)
		{
			e.interpret(_context);
		}
		return _context.pop();
	}		
}