Kotlin - How to recursively call a lambda function - recursion

Question

I'm trying to re implement the linrec function from here in Kotlin. Here is what it currently looks like in Kotlin:
fun <A, B> linrec(indivisible: (List<A>) -> Boolean,
value: (List<A>) -> B,
divide: (List<A>) -> List<List<A>>,
combine: (A, B) -> B
) : (List<A>) -> B {
val myfunc: (List<A>) -> B = { input ->
if (indivisible(input)) {
value(input)
} else {
val split = divide(input)
val left = split[0][0]
val right = myfunc(split[1]) // Error
combine(left, right)
}
}
return myfunc
}
IntelliJ gives me the following errors, when I try to run the code:
Error:(40, 19) Kotlin: Unresolved reference: myfunc
My question is: How do I make a lambda function call itself?

Answer 1

You don't call a lambda ("anonymous function") from inside itself. That's what functions are for:
fun <A, B> linrec(indivisible: (List<A>) -> Boolean,
value: (List<A>) -> B,
divide: (List<A>) -> List<List<A>>,
combine: (A, A) -> B
) : (List<A>) -> B {
fun myfunc(input: List<A>): B { // rearranged things here
return if (indivisible(input)) { // added `return`
value(input)
} else {
val split = divide(input)
val left = split[0][0]
val right = myfunc(split[1])
combine(left, right) // *
}
}
return ::myfunc
}
Now this is exactly the code you've wrote, but it does not compile. On the line I marked with * kotlinc says Type mismatch: inferred type is B but A was expected.
P.S. I have no idea what that code is doing, so I only fixed the compilation error you've asked about.