How to call 2 functions recursively? [duplicate]

Question

This question already has answers here:

How to have two methods calling each other? (4 answers)

Closed 9 years ago.

I have two functions :

let fn2 =
  if "something happend" then
    fn1

let rec fn1 =
  if "something" then
    fn2

This is just an example, what I am trying to do. Is there any Idea how to do it?

or should I just send the 2. function to the 1. function as parameter?

Answer 1

You need to use let rec ... and ...:

let rec fn1 x =
    if x = "something" then
        fn2 x
and fn2 x =
    if x = "something else" then
        fn1 x

Answer 2

You can also nest wrap your functions and create two higher-order-functions that take a function as an argument and apply it.

This could than be sth. like:

let fn2 fn =
  if "something happend" then
    fn fn2

let rec fn1 fn =
  if "something" then
    fn fn1

You can call than call your function like this:

let result = fn1 fn2

If you want your function to be more explicit your can write it for example like:

let rec fn2 (fn:unit->unit) : unit =
  if "something happend" then
    fn fn2

let rec fn1 (fn:unit->unit) : unit =
  if "something" then
    fn fn1

But I think kvb's answer is they better way to go because it is more standard-conform and readable.