calculator.js

/**
 * S-Expression Calculator
 * 
 */

// Start the function using node calculator.js 

// Process argument from the command line
let expr = process.argv[2];

// Function receives parsed expression from function below to determine add/multiply
function process_s_exp(parsed_exp) {  
  if (parsed_exp[0] === 'add') {
    return process_s_exp(parsed_exp[1]) + process_s_exp(parsed_exp[2]);
  } else if (parsed_exp[0] === 'multiply') {
    return process_s_exp(parsed_exp[1]) * process_s_exp(parsed_exp[2]);
  } else if (Array.isArray(parsed_exp[0])) {
    return process_s_exp(parsed_exp[0]);
  } else {
    return parseInt(parsed_exp);
  }
}

//Parsed through the string going character by character
function parse_s_expression(expr) {
  let parsedExp = [[]];
  let word = '';

//Used brackets/spaces to determine location of characters. Pushed characters to word to form add/multiply
  for (char in expr) {
    if (expr[char] === '(') {
      parsedExp.push([]);
    } else if (expr[char] === ')') {
      if (word) {
        parsedExp[parsedExp.length - 1].push(word);
        word = '';
      }
      let temp = parsedExp.pop()
      parsedExp[parsedExp.length - 1].push(temp);
    } else if (expr[char] === ' ') {
      if (word) {
        parsedExp[parsedExp.length - 1].push(word)
        word = ''
      }
    } else {
      word += expr[char];
    }
  }
//Once word is formed, add/multiply is given to process_s_exp to calculate integers 
  return parsedExp[0];
  
}

console.log(process_s_exp(parse_s_expression(expr)));