I'm trying to use Roman Elizarov's deep recursion ...

# coroutines

[snowe]

I'm trying to use Roman Elizarov's deep recursion implementation with coroutines (https://medium.com/@elizarov/deep-recursion-with-coroutines-7c53e15993e3), but am having a bit of an issue with calling methods from within the recursion function.

I'm attempting to use the implementation without modifying it (in the hopes that it is added to the stdlib some day.

Say I have this setup.

private suspend fun DeepRecursiveScope<Any?, Unit>.ppAny(obj: Any?) {
    DeepRecursiveFunction<Any?, Unit> { obj ->
        ppObj(obj)
    }
}

private suspend fun DeepRecursiveScope<Any?, Unit>.ppObj(obj: Any) {
    ppAny(obj)
}

I need to declare both as suspend and both as extension functions in order for them to be callable from within the DeepRecursiveScope. But ppAny is not callable from within ppObj, with the error

[NON_LOCAL_SUSPENSION_POINT] Suspension functions can be called only within coroutine body

Now, I understand the issue (I think), in that I need to be calling from within a context with, with(this@DeepRecursiveScopeImpl), but I do not have access to DeepRecursiveScopeImpl. Can I use another scope for this? If not, how can I get access to this scope to call my method with? Am I doing stuff completely wrong here???

[elizarov]

What exactly are you trying to achieve? I cannot decipher your intent from the code you've posted. What is its goal?

[snowe]

@elizarov the goal is to simply call other methods from within the recursion. You can see my library code here https://github.com/snowe2010/pretty-print/blob/master/src/main/kotlin/com/tylerthrailkill/helpers/prettyprint/PrettyPrint.kt

The entry point into the recursion is here: https://github.com/snowe2010/pretty-print/blob/master/src/main/kotlin/com/tylerthrailkill/helpers/prettyprint/PrettyPrint.kt#L63

You can see that ppAny calls different methods at this spot

https://github.com/snowe2010/pretty-print/blob/master/src/main/kotlin/com/tylerthrailkill/helpers/prettyprint/PrettyPrint.kt#L91-L96

and then those methods call back to ppAny like so

https://github.com/snowe2010/pretty-print/blob/master/src/main/kotlin/com/tylerthrailkill/helpers/prettyprint/PrettyPrint.kt#L139

But if I switch to the DeepRecursiveFunction, I cannot call those methods. I have to add them as extension methods on DeepRecursiveFunction. If I do that, then I cannot call callRecursive because the scope is not correct.

[elizarov]

There are two ways to declare recursive functions in this framework:

val first = DeepRecursiveFunction<A,B> { a -> .... }
suspend fun DeepRecursiveScope<*, *>.second(a: A): B { ... }

You need to at least one of the first kind to call it from the outside of your recursive computation via first(a) . Now inside any of those functions you call the first one via first.callRecursive(a) and the second one via second(a). That's it.

[elizarov]

If you are just calling utility functions that are not calling into the recursion you don't have to do anything -- these are just regular functions.

[snowe]

ah, ok, let me try that. Thank you.

[snowe]

I think I must still be misunderstanding something, as I am still getting that error.

[snowe]

@elizarov any clue what I'm doing wrong here?

[elizarov]

The lambda that you pass to ppContents function must be declared as an extension suspending function on DeepRecursiveScope. Alternatively, you can mark ppContents as inline.

[snowe]

Awesome. Got that working with your help thank you!. Now I can run out of heap space rather than Stack Overflows 😂