Interpreter

A way to include language elements in a program.

• Interpreter pattern provides a way to evaluate language grammar or expression.

• This pattern involves implementing an expression interface which tells to interpret a particular context.

• This pattern is used in SQL parsing, symbol processing engine etc.

• Interpreter contains the logic, which will convert the context to readable.

class TerminalExpression {	
   private data;
   constructor(String data){
      this.data = data; 
   }
   interpret(context) {   
      if(context.contains(data)){
         return true;
      }
      return false;
   }
}

class OrExpression {	 
   private expr1 = null;
   private expr2 = null;
   constructor(expr1, expr2) { 
      this.expr1 = expr1;
      this.expr2 = expr2;
   }
   interpret(context) {		
      return expr1.interpret(context) || expr2.interpret(context);
   }
}

class AndExpression {	 
   private expr1 = null;
   private expr2 = null;
   constructor(expr1, expr2) { 
      this.expr1 = expr1;
      this.expr2 = expr2;
   }
   interpret(String context) {		
      return expr1.interpret(context) && expr2.interpret(context);
   }
}

class InterpreterPatternDemo {

   //Rule: Robert and John are male
   static getMaleExpression(){
      const robert = new TerminalExpression("Robert");
      const john = new TerminalExpression("John");
      return new OrExpression(robert, john);		
   }

   //Rule: Julie is a married women
   static getMarriedWomanExpression(){
      const julie = new TerminalExpression("Julie");
      married = new TerminalExpression("Married");
      const return new AndExpression(julie, married);		
   }

   static run(args) {
      const isMale = getMaleExpression();
      const isMarriedWoman = getMarriedWomanExpression();

      console.log("John is male? " + isMale.interpret("John"));
      console.log("Julie is a married women? " + isMarriedWoman.interpret("Married Julie"));
   }
}

InterpreterPatternDemo.run();
// John is male? true
// Julie is a married women? true

EX2:

Interpreter Pattern