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名稱	Interpreter
結構
意圖	給定一個語言，定義它的文法的一種表示，并定義一個解釋器，這個解釋器使用該表示來解釋語言中的句子。
適用性	當有一個語言需要解釋執行, 并且你可將該語言中的句子表示為一個抽象語法樹時，可使用解釋器模式。而當存在以下情況時該模式效果最好：該文法簡單對于復雜的文法, 文法的類層次變得龐大而無法管理。此時語法分析程序生成器這樣的工具是更好的選擇。它們無需構建抽象語法樹即可解釋表達式, 這樣可以節省空間而且還可能節省時間。效率不是一個關鍵問題最高效的解釋器通常不是通過直接解釋語法分析樹實現的, 而是首先將它們轉換成另一種形式。例如，正則表達式通常被轉換成狀態機。但即使在這種情況下, 轉換器仍可用解釋器模式實現, 該模式仍是有用的。

Code Example

namespace?Interpreter_DesignPattern

{

????using?System;

????using?System.Collections;

????class?Context?

????{

????????

????}

????abstract?class?AbstractExpression?

????{

????????abstract?public?void?Interpret(Context?c);

????}

????//?class?for?terminal?symbol

????class?TerminalExpression?:?AbstractExpression

????{

????????override?public?void?Interpret(Context?c)????

????????{

????????????

????????}

????}

????//?class?for?grammar?rule?(one?per?rule?needed)

????class?NonterminalExpression?:?AbstractExpression

????{

????????override?public?void?Interpret(Context?c)????

????????{

????????????

????????}????

????}

????//?to?extend?grammar,?just?add?other?NonterminalExpression?classes

????///?<summary>

????///????Summary?description?for?Client.

????///?</summary>

????public?class?Client

????{

????????public?static?int?Main(string[]?args)

????????{

????????????Context?c?=?new?Context();

????????????ArrayList?l?=?new?ArrayList();?//really?need?a?tree?here!

????????????//?build?up?context?information?

????????????//?.?.?.

????????????//?Populate?abstract?syntax?tree?with?data

????????????l.Add(new?TerminalExpression());

????????????l.Add(new?NonterminalExpression());

????????????//?interpret

????????????foreach?(AbstractExpression?exp?in?l)

????????????{

????????????????exp.Interpret(c);

????????????}

????????????????????

????????????return?0;

????????}

????}

}

解析表達式:

//?Interpreter?pattern?--?Real?World?example??

using?System;

using?System.Collections;

namespace?DoFactory.GangOfFour.Interpreter.RealWorld

{

??//?MainApp?test?application?

??class?MainApp

??{

????static?void?Main()

????{

??????string?roman?=?"MCMXXVIII";

??????Context?context?=?new?Context(roman);

??????//?Build?the?'parse?tree'?

??????ArrayList?tree?=?new?ArrayList();

??????tree.Add(new?ThousandExpression());

??????tree.Add(new?HundredExpression());

??????tree.Add(new?TenExpression());

??????tree.Add(new?OneExpression());

??????//?Interpret?

??????foreach?(Expression?exp?in?tree)

??????{

????????exp.Interpret(context);

??????}

??????Console.WriteLine("{0}?=?{1}",?

????????roman,?context.Output);

??????//?Wait?for?user?

??????Console.Read();

????}

??}

??//?"Context"?

??class?Context

??{

????private?string?input;

????private?int?output;

????//?Constructor?

????public?Context(string?input)

????{

??????this.input?=?input;

????}

????//?Properties?

????public?string?Input

????{

??????get{?return?input;?}

??????set{?input?=?value;?}

????}

????public?int?Output

????{

??????get{?return?output;?}

??????set{?output?=?value;?}

????}

??}

??//?"AbstractExpression"?

??abstract?class?Expression

??{

????public?void?Interpret(Context?context)

????{

??????if?(context.Input.Length?==?0)?

????????return;

??????if?(context.Input.StartsWith(Nine()))

??????{

????????context.Output?+=?(9?*?Multiplier());

????????context.Input?=?context.Input.Substring(2);

??????}

??????else?if?(context.Input.StartsWith(Four()))

??????{

????????context.Output?+=?(4?*?Multiplier());

????????context.Input?=?context.Input.Substring(2);

??????}

??????else?if?(context.Input.StartsWith(Five()))

??????{

????????context.Output?+=?(5?*?Multiplier());

????????context.Input?=?context.Input.Substring(1);

??????}

??????while?(context.Input.StartsWith(One()))

??????{

????????context.Output?+=?(1?*?Multiplier());

????????context.Input?=?context.Input.Substring(1);

??????}

????}

????public?abstract?string?One();

????public?abstract?string?Four();

????public?abstract?string?Five();

????public?abstract?string?Nine();

????public?abstract?int?Multiplier();

??}

??//?Thousand?checks?for?the?Roman?Numeral?M?

??//?"TerminalExpression"?

??class?ThousandExpression?:?Expression

??{

????public?override?string?One()?{?return?"M";?}

????public?override?string?Four(){?return?"?";?}

????public?override?string?Five(){?return?"?";?}

????public?override?string?Nine(){?return?"?";?}

????public?override?int?Multiplier()?{?return?1000;?}

??}

??//?Hundred?checks?C,?CD,?D?or?CM?

??//?"TerminalExpression"?

??class?HundredExpression?:?Expression

??{

????public?override?string?One()?{?return?"C";?}

????public?override?string?Four(){?return?"CD";?}

????public?override?string?Five(){?return?"D";?}

????public?override?string?Nine(){?return?"CM";?}

????public?override?int?Multiplier()?{?return?100;?}

??}

??//?Ten?checks?for?X,?XL,?L?and?XC?

??//?"TerminalExpression"?

??class?TenExpression?:?Expression

??{

????public?override?string?One()?{?return?"X";?}

????public?override?string?Four(){?return?"XL";?}

????public?override?string?Five(){?return?"L";?}

????public?override?string?Nine(){?return?"XC";?}

????public?override?int?Multiplier()?{?return?10;?}

??}

??//?One?checks?for?I,?II,?III,?IV,?V,?VI,?VI,?VII,?VIII,?IX?

??//?"TerminalExpression"?

??class?OneExpression?:?Expression

??{

????public?override?string?One()?{?return?"I";?}

????public?override?string?Four(){?return?"IV";?}

????public?override?string?Five(){?return?"V";?}

????public?override?string?Nine(){?return?"IX";?}

????public?override?int?Multiplier()?{?return?1;?}

??}

}

Output

MCMXXVIII = 1928

posted on 2006-01-03 16:02 夢在天涯閱讀(924) 評論(0) 編輯收藏引用所屬分類: Design pattern

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