(slightly edited from initial version)

#![feature(macro_metavar_expr_concat)]
#![feature(macro_metavar_expr)]

macro_rules! gen_enums {
    ([$($name:ident)+]) => {
        gen_enums!(${count($name)}: [$($name)+]);
    };
    ($n:literal: [$($name:ident)+]) => {
        enum ${concat(Position, $n)} { $($name,)+ }
    };
    ($name:ident, $($tail:ident,)*) => {
        gen_enums!([$name $($tail)*]);
        gen_enums!($($tail,)*);
    };
    () => {};
}