How can I solve this type mismatch in Scala?

Question

 def balance(chars: List[Char]): Boolean = { if (chars.isEmpty == true) true else transCount(chars, 0) def transCount(chars: List[Char], pro: Int): Boolean = { var dif = pro chars match { case "(" :: Nil => false case ")" :: Nil => dif -= 1; if (dif == 0) true else false case _ :: Nil => if (dif == 0) true else false case "(" :: tail => dif += 1 transCount(tail, dif) case ")" :: tail => dif -= 1; if (dif < 0) false else transCount(tail, dif) case _ :: tail => transCount(tail, dif) } } }

I have the type mismatch problem

Error:(30, 13) type mismatch; found : String("(") required: Char case "(" :: Nil => false ^

but really do not know how to fix (do not use char.toList please)

Char literals use single quotes so you need to use case '(' :: Nil => false ... instead. — Lee
– Lee, Commented Mar 28, 2015 at 19:06

DNA · Accepted Answer · 2015-03-28 19:32:12Z

chars is declared as a List[Char].

However, your first pattern is "(" :: Nil, which is a List[String] because "(" is a String - hence the type mismatch.

You need a character literal '(', not a String literal "("

The same applies to the other patterns, of course.

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