Detect if a string has balanced parens

detect_balanced_parens.rb

#!/usr/bin/ruby

def isBalanced(string)
  stack = []
  string.split("").each do |i|
    if i == '('
      stack.push i 
    elsif i == ')'
      popped = stack.pop 
      return false if popped == nil
    else
      return false
    end
  end
  stack.empty?
end

if isBalanced(ARGV[0])
  puts "Balanced" 
else
  puts "Not balanced"
end