one of the alternatives to Go's error handling that OP writes about is the Rust Result type, which is the same as Either. OP seems to think this is the best of

one of the alternatives to Go's error handling that OP writes about is the Rust Result type, which is the same as Either. OP seems to think this is the best of the alternatives to the way Go handles things, but that switching to a sum-type approach would be too difficult, given that it isn't compatible in any way with normal Go error checking and a lot of software has already been written in the old style.