Sum types allow a function to return either a result or an error. Not accounting for both possibilities is a compile time type error. Go mimics this behavior,

Sum types allow a function to return either a result or an error. Not accounting for both possibilities is a compile time type error. Go mimics this behavior, so it's not only a functional thing: http://blog.golang.org/error-handling-and-go http://blog.golang.org/error-handling-and-go