object Main extends App
{
  def f(acc : Map[Char, String], s: String) = acc.+((s.head, s))
  val myList = List("abc", "bcd", "cde", "def", "efg")
  val w = myList.fold(Map[Char, String]())(f)
  print(w)
}

/*
Error:(5, 44) type mismatch;
 found   : (Map[Char,String], String) => scala.collection.immutable.Map[Char,String]
 required: (Object, Object) => Object
  val w = myList.fold(Map[Char, String]())(f)
*/