When it's occasionally useful return (type, err), but generally the two results are distinct so there's no need to return two results in the general case when one suffices

Indeed, I recently updated some code to return a relevant value in the error case: https://github.com/wal-g/wal-g/pull/1143/files#diff-d896e5d5... where true means the error is rooted in a corrupted page, & false means that the error isn't due to a corrupted page. It does feel a little dirty & a comment is probably necessary to make this case clear

Still, Result can work here. For example, Rust's binary_search https://doc.rust-lang.org/std/vec/struct.Vec.html#method.bin... which returns Ok(idx) when that's the location of the element, or Err(idx) when that's the location the element would be if it were there (this can be a bit annoying when you just want to insert, since you end up writing `let idx = match result { Ok(idx) => idx, Err(idx) => idx }`)