How to return a function in scala

Question

How can I return a function side-effecting lexical closure¹ in Scala?

For instance, I was looking at this code sample in Go:

Answer 1

While we're sharing cool implementations of the fibonacci function that are only tangentially related to the question, here's a memoized version:

val fib: Int => BigInt = {                         
   def fibRec(f: Int => BigInt)(n: Int): BigInt = {
      if (n == 0) 1 
      else if (n == 1) 1 
      else (f(n-1) + f(n-2))                           
   }                                                     
   Memoize.Y(fibRec)
}

It uses the memoizing fixed-point combinator implemented as an answer to this question: In Scala 2.8, what type to use to store an in-memory mutable data table?

Incidentally, the implementation of the combinator suggests a slightly more explicit technique for implementing your function side-effecting lexical closure:

def fib(): () => Int = {
   var a = 0
   var b = 1
   def f(): Int = {
      val t = a;
      a = b
      b = t + b
      b
  }
  f
}