Macro infix 

macro_rules! infix {
    (
        $name:ident: $output:ty;
        $($atom_val:ident : $atom:expr => $atom_ex:expr;)+
        $(
            @[$type:ident $(($($vars:tt)*))?]
            $($op:expr => $ex:expr;)+
        )*
    ) => { ... };
}

Automatically generate a parser for infix expressions, using precedence climbing.