When will Rust have TCO/TCE?

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3

This won't help for general tail calls, but if you can just use tail recursion, you can use a combinator:

pub fn factorial(x: usize) -> usize {
    tail_recurse((x, 1), |(a, b)| {
        if a == 0 { RecursionResult::Return(b) }
        else { RecursionResult::Continue((a - 1, a * b)) }
    })
}

Amusingly, that actually generates better code than (1..=x).product() :laughing:

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