'''
    CS5001
    Fall 2018
    Sample code: using a stack as the only data structure,
    determine whether an input string has balanced parentheses.
    Definition of balanced:
    * () is balanced
    * if x is balanced, then (x) is balanced
    * if x and y are balanced, then xy is balanced.
'''

from mystax import Stack

def is_balanced(string):
    ''' Function is_balanced
        Input: string (a string)
        Returns: True if balanced open/close parens, false otherwise
    '''
    stack = Stack()

    for char in string:
        if char == "(":
            stack.push(char)
        elif char == ")":
            if stack.is_empty():
                return False
            stack.pop()

    if stack.is_empty():
        return True
    return False