Behavioural Design Pattern: Interpreter Design pattern

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.