How to do recursive loops in scala

Question

I was wondering if there is a better way to write recursive loops in scala.

def fib(n: Int) = {
  def loop(a: BigInt = 0, b: BigInt = 1, n: Int = n): BigInt = {
    if(n==0) a
    else loop(b, a+b, n-1)
  }
  loop()
}

I could write it like this

def fib(n: Int, a: BigInt = 0, b: BigInt = 1): BigInt = {
  if(n==0) a
  else fib(n-1, b, a+b)
}

but then a and b would be exposed and not encapsulated inside the method anymore.

Answer 1

Note that you can often use foldLeft or foldRight in such situations:

def fib(n: Int) = (1 to n).foldLeft((BigInt(0),BigInt(1)))((p,_)=>(p._2,p._1+p._2))._1

[Edit]

Another approach would be an iterator-based solution:

def fib = Iterator.iterate((0,1)){case (x,y) => (y,x+y)}.map(_._1)

This generates an infinite amount of fibonacci numbers, but you can simply take as many as you want from it, e.g. fib.take(10).toList

Answer 2

Loops have their own scopes. When you replace a loop with a recursive function you are forced to create an explicit scope (the inner method). There is no way around it. This is how it is done. Nothing wrong about it.