Scala way to program bunch of if's

Question

I\'m starting out with scala, and trying to apply the functional way to it, but I came out with bunch of nested if\\else constructions which is hard to read, and I wonder is

Answer 1

Well:

1. You could start by writing it with else if conditions.
2. Go ahead an annotate it with tailrec since it's tail-recursive.
3. The filter condition can be written more simply as Set('(', ')'), which is a function from Char to Boolean
4. I think you're missing the condition where chars is empty but parenthesis is not.

So it would look like:

def balance(chars: List[Char]): Boolean = {
  @tailrec
  def checkParentesys(chars: List[Char], parentesis: List[Char]): Boolean =
    if (chars.isEmpty && parentesis.isEmpty)
      true
    else if (chars.head == '(')
      checkParentesys(chars.tail, '(' :: parentesis)
    else if (chars.isEmpty || parentesis.isEmpty)
      false
    else
      checkParentesys(chars.tail, parentesis.tail)

  checkParentesys(chars.filter(Set('(', ')')), List())
}

You could also just turn the whole thing into a pattern match:

def balance(chars: List[Char]): Boolean = {
  @tailrec
  def checkParentesys(chars: List[Char], parentesis: List[Char]): Boolean =
    (chars, parentesis) match {
      case (Nil, Nil) => true
      case ('(' :: charsTail, _) => checkParentesys(charsTail, '(' :: parentesis)
      case (Nil, _) => false
      case (_, Nil) => false
      case (')' :: charsTail, '(' :: parentesisTail) => checkParentesys(charsTail, parentesisTail)
    }
  checkParentesys(chars.filter(Set('(', ')')), List())
}