In this article, we will learn how to use and implement the Interpreter Pattern in TypeScript with an example.

Interpreter pattern provides a way to evaluate language grammar or expression. This type of pattern comes under behavioral patterns. This pattern involves implementing an expression interface which tells to interpret a particular context.

TypeScript Interpreter Design Pattern Example

Let's create interpreter.ts file and add the following code to it:

export class Context {
}

export interface AbstractExpression {
    interpret(context: Context): void;
}

export class TerminalExpression implements AbstractExpression {
    public interpret(context: Context): void {
        console.log("`interpret` method of TerminalExpression is being called!");
    }
}

export class NonterminalExpression implements AbstractExpression {

    public interpret(context: Context): void {
        console.log("`interpret` method of NonterminalExpression is being called!");
    }
}

Usage

Let's create demo.ts file and add the following code to it:

import { NonterminalExpression, TerminalExpression, Context } from "./interpreter";

export function show() : void {
 var context: Context = new Context(),
  list = [],
  i = 0,
  max;

 list.push(new NonterminalExpression());
 list.push(new NonterminalExpression());
 list.push(new NonterminalExpression());
 list.push(new TerminalExpression());
 list.push(new NonterminalExpression());
 list.push(new NonterminalExpression());
 list.push(new TerminalExpression());
 list.push(new TerminalExpression());

 for (i = 0, max = list.length; i < max; i += 1) {
  list[i].interpret(context);
 }
}
show();

Run:

• Compile the above code using the TypeScript compiler.
• Above code is compiled to plan JavaScript code
• Run Javascript code using node

design_patterns_in_typescript\interpreter> tsc --target ES5 .\demo.ts
design_patterns_in_typescript\interpreter> node .\demo.js
`interpret` method of NonterminalExpression is being called!
`interpret` method of NonterminalExpression is being called!
`interpret` method of NonterminalExpression is being called!
`interpret` method of TerminalExpression is being called!
`interpret` method of NonterminalExpression is being called!
`interpret` method of NonterminalExpression is being called!
`interpret` method of TerminalExpression is being called!
`interpret` method of TerminalExpression is being called!

All TypeScript Design Patterns

1. Creational Design Patterns

Creational patterns provide various object creation mechanisms, which increase flexibility and reuse of existing code.

1. TypeScript Singleton Pattern Example
2. TypeScript Factory Design Pattern with Example
3. TypeScript Abstract Factory Pattern Example
4. TypeScript Builder Pattern Example
5. TypeScript Prototype Pattern Example

2. Structural Design Patterns

Structural patterns explain how to assemble objects and classes into larger structures while keeping these structures flexible and efficient.

1. TypeScript Bridge Pattern Example
2. TypeScript Adapter Pattern Example
3. TypeScript Decorator Pattern Example
4. TypeScript Composite Pattern Example
5. TypeScript Flyweight Design Pattern Example
6. TypeScript Facade Pattern Example
7. TypeScript Proxy Pattern Example

3. Behavioral Design Patterns

Behavioral design patterns are concerned with algorithms and the assignment of responsibilities between objects.

1. TypeScript Command Pattern Example
2. TypeScript Chain of Responsibility Pattern Example
3. TypeScript Visitor Pattern Example
4. TypeScript Template Method Pattern Example
5. TypeScript Strategy Pattern Example
6. TypeScript State Pattern Example
7. TypeScript Observer Pattern Example
8. TypeScript Memento Pattern Example
9. TypeScript Mediator Pattern Example
10. TypeScript Iterator Pattern Example
11. TypeScript Interpreter Design Pattern Example

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