Enumerable types for errors in Os package

[raviqqe]

Problem

• Errors from an Os package is difficult to distinguish because they are error messages of strings.
• For example, we cannot handle recoverable errors on clients.

Solution

• Use enumerable types for errors in an Os package.

Examples

type OperationNotPermitted{}
type NoSuchFileOrDirectory{}
...

type Error =
  OperationNotPermitted |
  NoSuchFileOrDirectory |
  ...

Format = \(e Error) string {
  ...
}