tree-flatten-macro.rs

macro_rules! const1 {
    ($id:ident, $depth:expr, [$($prefix:tt)*])
        =>
    {
        const $id: [&'static str; $depth] = [$($prefix),*];
    };
}

macro_rules! const_tree_at {
    ($depth:tt ;
     [$($prefix:tt)*] ;
     ;)
        =>
    { };

    ($depth:tt ;
     [$($prefix:tt)*] ;
     { })
        =>
    { };

    ($depth:tt ;
     [$($prefix:tt)*] ;
     { $name:tt => $id:ident $subtree:tt $($more:tt)* })
        =>
    {
        const1!($id, ($depth + 1), [$($prefix)* $name]);
        const_tree_at!(($depth + 1) ; [ $($prefix)* $name ] ; $subtree);
        const_tree_at!($depth ; [$($prefix)*] ; { $($more)* });
    };
}

macro_rules! const_tree {
    ($($t:tt)*) => {
        const_tree_at!(0 ; [] ; { $($t)* });
    };
}