[dymk]

> Often in Go, errors are used to mark different states, such as EOF which are expected

Then it's not an error, and Go has once again forced people into writing something semantically confusing and/or incorrect because it lacks basic abstractions.

[bouncycastle]

Actually, any type can be an error, just as long as it impliments the Error interface. Go is more about interfaces - if some type impliments some interface, then that's what it is.