Shared via Rust Playground

playground.rs

macro_rules! trn {
    (@parse () -> (($a:expr) ($b:expr) ($c:expr))) => {
        if $a { $b } else { $c }
    };
    
    (@parse (? $head:tt $($tail:tt)*) -> ($a:tt () ())) => {
        trn!(@parse ($($tail)*) -> ($a ($head) ()))
    };
    (@parse (: $head:tt $($tail:tt)*) -> ($a:tt $b:tt ())) => {
        trn!(@parse ($($tail)*) -> ($a $b ($head)))
    };
    
    (@parse ($head:tt $($tail:tt)*) -> (($($a:tt)*) () ())) => {
        trn!(@parse ($($tail)*) -> (($($a)* $head) () ()))
    };
    (@parse ($head:tt $($tail:tt)*) -> ($a:tt ($($b:tt)*) ())) => {
        trn!(@parse ($($tail)*) -> ($a ($($b)* $head) ()))
    };
    (@parse ($head:tt $($tail:tt)*) -> ($a:tt $b:tt ($($c:tt)*))) => {
        trn!(@parse ($($tail)*) -> ($a $b ($($c)* $head)))
    };
    
    ($($t:tt)*) => {
        trn!(@parse ($($t)*) -> (() () ()))
    }
}

fn main() {
    println!("{}", trn!(false ? 1 : trn!(false ? 2 : 3)));
}