JavaScript Example

// contains the information that will be interpreted
class Context {
  constructor(value) {
    this.v = value;
  }
}

module.exports = Context;

// provide specific conversions on different types of data
class MinusNonTerminalExpression {
  constructor(numA, numB) {
    this.numA = numA;
    this.numB = numB;
  }

  interpret(context) {
    return this.numA.interpret(context) - this.numB.interpret(context);
  }
}

module.exports = MinusNonTerminalExpression;

// provide specific conversions on different types of data
class NumberTerminalExpression {
  constructor(num) {
    this.num = num;
  }

  interpret(context) {
    return this.num;
  }
}

module.exports = NumberTerminalExpression;

// provide specific conversions on different types of data
class TimesNonTerminalExpression {
  constructor(numA, numB) {
    this.numA = numA;
    this.numB = numB;
  }

  interpret(context) {
    return this.numA.interpret(context) * this.numB.interpret(context);
  }
}

module.exports = TimesNonTerminalExpression;

// provide specific conversions on different types of data
class VariableTerminalExpression {
  constructor(variable) {
    this.variable = variable;
  }

  interpret(context) {
    return context[this.variable] || 0;
  }
}

module.exports = VariableTerminalExpression;

const Context = require("./Context");
const NumberTerminalExpression = require("./NumberTerminalExpression");
const VariableTerminalExpression = require("./VariableTerminalExpression");
const TimesNonTerminalExpression = require("./TimesNonTerminalExpression");
const MinusNonTerminalExpression = require("./MinusNonTerminalExpression");

class Client {
  constructor(context) {
    this.context = context;
  }

  parse(expression) {
    const values = expression.split(" ");
    const queue = [];
    let exp;
    let numB;
    let numA;
    for (const value of values) {
      switch (value) {
        case "*":
          numB = queue.pop();
          numA = queue.pop();
          exp = new TimesNonTerminalExpression(numA, numB);
          break;
        case "-":
          numB = queue.pop();
          numA = queue.pop();
          exp = new MinusNonTerminalExpression(numA, numB);
          break;
        default:
          if (isNaN(parseInt(value))) {
            exp = new VariableTerminalExpression(value);
          } else {
            const number = parseInt(value);
            exp = new NumberTerminalExpression(number);
          }
          break;
      }
      queue.push(exp);
    }
    const main = queue.pop();
    return main.interpret(this.context);
  }
}

const ctxt = new Context(45);
const res = new Client(ctxt).parse("16 v * 76 q - -");
console.log(res);