Question

This compiles:

 def fibonacci():() => Int = {
        var first   = 1
        var second  = 2
        return () => {
            val oldFirst = first
            first = second
            second = second + oldFirst
            second 
        }
    }

This doesn’t:

 def fibonacci():() => Int = {
     var first   = 1
     var second  = 2
     return ():Int => {
         val oldFirst = first
         first = second
         second = second + oldFirst
         second 
     }
 }

I am explicitly trying to tell it that I’m returning an Int, but I get this error: Illegal start of declaration, and it’s pointing to the first = second line. How are they different? I am using Scala 2.8.1.

Answer 1

return (): Int => {...} is not a proper expression in Scala. If you wanted to specify the return type explicitly, you’ll need to put the declaration after the value (and the value would be the anonymous function):

def fibonacci():() => Int = {
  var first   = 1
  var second  = 2
  return ( () => {
    val oldFirst = first
    first = second
    second = second + oldFirst
    second 
  } ) : () => Int
}

Note, however, that there is no need in doing that. If you omit return, you do not need to make any explicit type declaration at all:

def fibonacci() = {
  var first   = 1
  var second  = 2
  () => {
    val oldFirst = first
    first = second
    second = second + oldFirst
    second 
  }
}