# Recursive call vs while loop

**URL:** <https://discourse.julialang.org/t/recursive-call-vs-while-loop/7723>\
**Category:** Performance\
**Tags:** recursion\
**Created:** [December 12, 2017, 9:37pm UTC](https://discourse.julialang.org/t/recursive-call-vs-while-loop/7723 "2017-12-12T21:37:31Z")\
**Posts on this page:** 1\
**Showing post:** 17

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**Author:** ![zot](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/zot/32/5817_2.png) [@zot](https://discourse.julialang.org/u/zot)\
**Post date:** [October 31, 2018, 11:53am UTC](https://discourse.julialang.org/t/recursive-call-vs-while-loop/7723/17 "2018-10-31T11:53:59Z")

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> [@ihnorton](#):
>
> > [@dalejordan](#):
> >
> > The OP’s first example:
> 
> Which does return…

It’s not enough that the function just return, to be tail recursive, a function must return a naked recursive call. The OP’s first example doesn’t return a naked call, transforms the result by multiplying it by N.

A tail recursive version of factorial would have to use an accumulator:

```julia
factorial(::Type{Val{0}}, acc) = acc
factorial(::Type{Val{N}}, acc) where N = factorial(Val{N - 1}, N * acc)
factorial(n) = factorial(Val{n}, 1)

```

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