Behavioural Design Pattern: Interpreter Design pattern

Level : Advanced
Mentor: Shailendra Chauhan
Duration : 00:01:00

Define Interpreter Design pattern

This pattern evaluates and interprets instructions (Source Code) written in a language's grammar or notation. Implementing an expression interface instructs how to comprehend a specific context.

Examples of Interpreter Pattern

Examples of interpreter patterns are:

  • Language Compiler
  • Language Interpreter/Translator
  • String/Data Parsing

Interpreter Pattern with UML Diagram

The classes, interfaces, and objects in the above UML class diagram are defined as follows.

  • Client: This class creates the abstract syntax tree for a collection of instructions in grammar. This tree is built using instances of the NonTerminalExpression and TerminalExpression classes.
  • Context: This is a class that stores information (input and output) for use by the Interpreter.
  • Expression: This interface defines the Interpret operation, which must be implemented by all subclasses.
  • NonTerminal: This class implements the Expression. This can include further instances of Expression.
  • Terminal: This class implements the Expression.

When should you use the Interpreter Design pattern?

The interpreter design pattern is beneficial in the following situations:

  • Interpret a grammar expressed as a big syntax tree.
  • Parsing tools are provided.
  • Efficiency is not an issue.

Advantages of the Interpreter Design Pattern

  • Easy to Change and Extend Grammars: Grammars are simple to update and enhance by introducing new expressions.
  • Separation of Concerns: Distinguishes the grammar definition and interpretation logic from the primary application logic.
  • Reusable Components: Grammar rules can be reused throughout the program.
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