给定一个语言,定义它的文法表示,并定义一个解释器,这个解释器使用该标识来解释语言中的 句子。
解释器模式包含以下主要角色
下面是一个简单的解释器模式的C#实现,这个例子中,我们将创建一个IExpression
接口和实现了IExpression
接口的具体类AddExpression
和SubtractExpression
。Context
是一个解释器上下文类,它将用于存储和管理解释器的状态。
抽象角色AbstractExpression
public interface AbstractExpression
{
public int interpret(Context context);
public string toString();
}
终结符表达式角色
public class Value : AbstractExpression
{
private int _value;
public Value(int value)
{
_value = value;
}
public int interpret(Context context)
{
return _value;
}
public string toString()
{
return _value.ToString();
}
}
非终结符表达式角色 加减法表达式
///
/// 加法
///
public class Plus : AbstractExpression
{
private AbstractExpression _left;
private AbstractExpression _right;
public Plus(AbstractExpression left, AbstractExpression right)
{
_left = left;
_right = right;
}
public int interpret(Context context)
{
return _left.interpret(context) + _right.interpret(context);
}
public String toString()
{
return "(" + _left.toString() + " + " + _right.toString() + ")";
}
}
///
/// 减法
///
public class Minus : AbstractExpression
{
private AbstractExpression _left;
private AbstractExpression _right;
public Minus(AbstractExpression left, AbstractExpression right)
{
_left = left;
_right = right;
}
public int interpret(Context context)
{
return _left.interpret(context) - _right.interpret(context);
}
public string toString()
{
return "(" + _left.toString() + " - " + _right.toString() + ")";
}
}
终结符表达式角色 变量表达式
public class Variable:AbstractExpression
{
private string _name;
public Variable(string name)
{
_name = name;
}
public int interpret(Context context)
{
return context.GetValue(this);
}
public string toString()
{
return _name;
}
}
环境(Context)角色
public class Context
{
private Dictionary map = new Dictionary();
public void Assign(Variable var, int value)
{
map[var] = value;
}
public int GetValue(Variable var)
{
int value = map[var];
return value;
}
}
测试类
class MyClass
{
public static void Main(string[] args)
{
Context context = new Context();
Variable a = new Variable("a");
Variable b = new Variable("b");
Variable c = new Variable("c");
Variable d = new Variable("d");
Variable e = new Variable("e");
context.Assign(a, 1);
context.Assign(b, 2);
context.Assign(c, 3);
context.Assign(d, 4);
context.Assign(e, 5);
AbstractExpression expression = new Minus(new Plus(new Plus(new
Plus(a, b), c), d), e);
Console.WriteLine(expression + "= " +
expression.interpret(context));
}
}
运行结果!
优点:
缺点:
使用场景: