gibo

/*
    
    
    
        A
      /   \
     B     C
    / \   / \
   D   E F   G
*/

gibo

// ** check for validate parenthesis

const isValidParenthesis = str => {
  let brackets = 0;
  for (let i = 0; i < str.length; i++) {
    if (str.charAt(i) === "(") {
      brackets++;
    } else if (str.charAt(i) === ")") {
      brackets--;
    } else {

gibo

Cons.fromArray = function(array) {
  array = array.reverse();
  let last = new Cons(array.shift(), null);
  array.forEach(function(item) {
    last = new Cons(item, last);
  });
  return last;
}