Macro parse_operator

macro_rules! parse_operator {
    (__impl
     $i: expr,
     // TODO: the final macro ideally wouldn't require type info
     <$ty: ty, $op_ty: ty>,
     $atom: path,
     $($ops:tt)*) => { ... };
    (__impl
     $i: expr,
     // TODO: the final macro ideally wouldn't require type info
     <$ty: ty, $op_ty: ty>,
     $atom: ident!( $($atom_args:tt)* ),
     $($ops:tt)*) => { ... };
    ($i: expr, <$ty: ty, $op_ty: ty>, $($rest:tt)* ) => { ... };
}

Parses an input expression according to the operators defined in the arguments