解释器模式（Interpreter Pattern）

解释器模式（Interpreter Pattern）是一种行为型模式，定义了一个解释器，来解释给定语言和文法的句子。其实质是把语言中的每个符号定义成一个（对象）类，从而把每个程序转换成一个具体的对象树。解释器模式的作用很强大，它使得改变和扩展文法变得容易，很多编译器，包括文本编辑器、网页浏览器及VRML都应用解释器模式。因文句会分析成树结构，解释器需要递归访问它，则效率会受影响。程序开发时会有所体会，编译整个工程源码耗费时间都比较长。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication
{

    //一般每个接口或类都写在单独的.cs文件中
    //本示例为了执行查看方便才写在一起
    /// <summary>
    /// 解释器抽象类
    /// </summary>
    abstract class AbstractionExpression
    {
        public abstract string Interpret();
    }
    /// <summary>
    /// 用于解释具体的某个指令
    /// </summary>
    class TerminalExpression : AbstractionExpression
    {
        AbstractionExpression _Dir, _RunMode, _Dis;
        public TerminalExpression(AbstractionExpression dir, AbstractionExpression runMode, AbstractionExpression dis)
        {
            this._Dir = dir;
            this._RunMode = runMode;
            this._Dis = dis;
        }
        public override string Interpret()
        {
            return string.Concat(_Dir.Interpret(), _RunMode.Interpret(), _Dis.Interpret());
        }

    }
    /// <summary>
    /// 用于将终结符表达式连接起来
    /// </summary>
    class NonTerminalExpression : AbstractionExpression
    {
        AbstractionExpression _Left, _Right;
        public NonTerminalExpression(AbstractionExpression left, AbstractionExpression right)
        {
            this._Left = left;
            this._Right = right;
        }
        public override string Interpret()
        {
            return $"{this._Left.Interpret()}然后{ this._Right.Interpret()} ";
        }
    }
    /// <summary>
    /// 终结符表达式中需要用到的表达式
    /// </summary>
    class DirExpression : AbstractionExpression
    {
        string _Dir;
        public DirExpression(string dir)
        {
            this._Dir = dir;
        }
        public override string Interpret()
        {
            if (this._Dir == "up")
            {
                return "向上";
            }
            else if (this._Dir == "down")
            {
                return "向下";
            }
            else if (this._Dir == "left")
            {
                return "向左";
            }
            else if (this._Dir == "right")
            {
                return "向右";
            }
            else
            {
                return "方向错误";
            }
        }
    }

    class RunModeExpression : AbstractionExpression
    {
        public string _RunMode;
        public RunModeExpression(string runMode)
        {
            this._RunMode = runMode;
        }
        public override string Interpret()
        {
            if (this._RunMode == "move")
            {
                return "移动";
            }
            else if (this._RunMode == "run")
            {
                return "快速移动";
            }
            else
            {
                return "运动模式错误";
            }

        }
    }


    class DisExpression : AbstractionExpression
    {
        string _Dis;
        public DisExpression(string dis)
        {
            this._Dis = dis;
        }
        public override string Interpret()
        {
            return $"距离为{this._Dis }";
        }
    }
    /// <summary>
    /// 上下文环境类
    /// </summary>
    public class HandleExpression
    {
        Stack<AbstractionExpression> stack = new Stack<AbstractionExpression>();//使用栈类实现递归
        AbstractionExpression _dir, _runMode, _dis;
        AbstractionExpression allExpression;
        public void Operate(string expression)
        {
            string[] str = expression.Split(' ');
            for (int i = 0; i < str.Length; i++)
            {
                if (str[i] == "and")
                {
                    AbstractionExpression left = stack.Pop();
                    _dir = new DirExpression(str[++i]);
                    _runMode = new RunModeExpression(str[++i]);
                    _dis = new DisExpression(str[++i]);
                    AbstractionExpression right = new TerminalExpression(_dir, _runMode, _dis);
                    AbstractionExpression endExpression = new NonTerminalExpression(left, right);
                    stack.Push(endExpression);
                }
                else
                {

                    _dir = new DirExpression(str[i]);
                    _runMode = new RunModeExpression(str[++i]);
                    _dis = new DisExpression(str[++i]);
                    AbstractionExpression endExpression = new TerminalExpression(_dir, _runMode, _dis);
                    stack.Push(endExpression);
                }
            }
            allExpression = stack.Pop();//弹出所有表达式
        }


        public string InterpretAll()
        {

            return allExpression.Interpret();
        }
    }

    class Program
    {

        static void Main(string[] args)
        {
            HandleExpression handleExpression = new HandleExpression();
            string expression = "up move 230 and down run 640";
            handleExpression.Operate(expression);
            string result = handleExpression.InterpretAll();
            Console.WriteLine(result);
            Console.ReadKey();
        }
    }
}