Scala function to get next letter of the alphabet

Question

Looking for something to do the following:

Given input: "s"
Expected output: "t"

Answer 1

scala> def f(s: String) = (s.head + 1).toChar.toString
f: (s: String)java.lang.String

scala> f("s")
res10: java.lang.String = t

Answer 2

def nextLetter(x:String) = (x(0) + 1).toChar.toString