Re: [Haskell-cafe] No Enum for (,), no Enum or Bounded for Either

Tom Ellis writes:

I'm a bit surprised that whilst `Either` and `(,)` have instances for `Ord`

* `(,)` has no instance for `Enum` * `Either` has no instance for `Enum` or `Bounded`

Is there a particular reason for that? It might be tricky to implement

toEnum :: Int -> a fromEnum :: a -> Int

but in the presence of `Bounded` that should be possible.

You don’t need Bounded to do that. For example, you could start at (0,0) and go out in diamond shaped rings. A more pressing reason is that there are too many possible enumerations, and if we picked one it would probably be the wrong one for most applications. -- Jón Fairbairn Jon.Fairbairn@cl.cam.ac.uk