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Interpreter mode (Interpreter): Given a language, define a representation of its grammar, and define an interpreter that uses the representation to interpret sentences in the language.
Problems solved by the interpreter pattern: If a particular type of problem occurs frequently enough, it may be worthwhile to express each instance of the problem as a sentence in a simple language. This makes it possible to build an interpreter that solves the problem by interpreting these sentences.
Regular expression is one of its applications. The interpreter defines a grammar for regular expressions and represents a specific regular expression, as well as how to interpret this regular expression.
Four roles:
AbstractExpression: declares an abstract interpretation operation. This interface is shared by all nodes in the abstract syntax tree.
TerminalExpression Terminal expression: implements the interpretation operation associated with the terminal symbols in the grammar.
NonterminalExpression: Nonterminal expression, which implements interpretation operations for nonterminal symbols in the grammar. A specific nonterminal expression class is required for each rule R1, R2...Rn in the grammar.
Context: Contains some global information outside the interpreter.
Mode implementation:
[code]//Context class Context{ private: std::string input; public: std::string Input(std::string in){ input = in; return input; } }; //抽象表达式 class AbstractExpression{ public: virtual void Interpret(Context *context) = 0; }; //终结符表达式 class TerminalExpression: public AbstractExpression{ public: void Interpret(Context *context)override{ std::cout << "TerminalExpression\n"; } }; //非终结符表达式 class NonterminalExpression: public AbstractExpression{ public: void Interpret(Context *context)override{ std::cout << "NonterminalExpression\n"; } };
Client:
[code]//Client int main(){ Context *context = new Context; std::list<AbstractExpression*> list; list.push_back(new TerminalExpression); list.push_back(new NonterminalExpression); list.push_back(new TerminalExpression); list.push_back(new TerminalExpression); for(auto i : list) i->Interpret(context); // Output: // TerminalExpression // NonterminalExpression // TerminalExpression // TerminalExpression return 0; }
Interpreter mode benefits:
Usually there is a language that needs to be interpreted and executed, and the language can be The interpreter mode can be used when the sentences in are represented as an abstract syntax tree.
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