Function signature for returning a recursive closure

I am attempting to implement a function that returns a recursive closure., though I am not sure how to express that in the function signature. Here is example code of a working implementation in Python

def counter(state):
    def handler(msg):
        if msg == 'inc':
            print state
            return counter(state + 1)

        if msg == 'dec':
            print state
            return counter(state - 1)
    return handler

c = counter(1)
for x in range(1000000):
    c = c('inc')

and pseudo code for Rust.

enum Msg {
    Inc,
    Dec
}

fn counter(state: Int) -> ? {
    move |msg| match msg {
        Msg::Inc => counter(state + 1),
        Msg::Dec => counter(state - 1),
    }
}