Interpreter Pattern 解释器模式

Definition

Given a language, define a representation for its grammar along with an interpreter that uses the representation to interpret sentences in the language.
给定一门语言，定义它的文法的一种表示，并定义一个解释器，该解释器使用该表示来解释语言中的句子。

Participants

The classes and objects participating in this pattern are:

AbstractExpression (Expression)

• declares an interface for executing an operation

TerminalExpression ( ThousandExpression, HundredExpression, TenExpression, OneExpression )

• implements an Interpret operation associated with terminal symbols in the grammar.
• an instance is required for every terminal symbol in the sentence.

NonterminalExpression ( not used )

• one such class is required for every rule R ::= R1R2...Rn in the grammar
• maintains instance variables of type AbstractExpression for each of the symbols R1 through Rn.
• implements an Interpret operation for nonterminal symbols in the grammar. Interpret typically calls itself recursively on the variables representing R1 through Rn.

Context (Context)

• contains information that is global to the interpreter

Client (InterpreterApp)

• builds (or is given) an abstract syntax tree representing a particular sentence in the language that the grammar defines. The abstract syntax tree is assembled from instances of the NonterminalExpression and TerminalExpression classes
• invokes the Interpret operation