Is nested function efficient?

Question

In programming languages like Scala or Lua, we can define nested functions such as

function factorial(n)
  function _fac(n, acc)
    if n == 0 then
      return          


        

Answer 1

I don't know about lua, but in Scala are very common and used in recursive functions to ensure tail-safe optimization:

def factorial(i: Int): Int = {
      @tailrec
     def fact(i: Int, accumulator: Int): Int = {
        if (i <= 1)
           accumulator
        else
           fact(i - 1, i * accumulator)
     }
     fact(i, 1)
  }

More info about tail-safe and recursion here