Check parentheses balancing on the "Functional Programming Principles in Scala" course in Coursera.

balance.coffee

balance = (charList) ->
  isBegin = (_char) -> _char == '('
  isEnd = (_char) -> _char == ')'
  
  check = (_counter,_char) ->
    return _counter+1 if isBegin(_char)
    return _counter-2 if isEnd(_char) and (_counter<=0)
    return _counter-1 if isEnd(_char)
    return _counter
    
  loops = (_counter, _charList) ->
    if _.isEmpty _charList
      return (_counter == 0)
    else
      loops(check(_counter, _.head _charList), (_.tail _charList))

  return loops(0,charList)

originText = "(ex)()am"

charList = _.toArray originText

console.log balance charList