os-string as a typeclass?

I've started writing a typeclass for all conversions:

```haskell
class ToOS a b where
toOS :: a -> b

instance ToOS ByteString OsString where
toOS = OsString . toOS

instance ToOS PosixPath OsString where
toOS = OsString

instance ToOS ByteString PosixPath where
toOS = coerce . BSS.toShort

instance ToOS PosixPath ByteString where
toOS = BSS.fromShort . coerce

...
```

Then I've realized that some of the conversions would raise an exception like `FilePath -> m PosixPath`.

On top of that, a lot of these conversions are `O(n)` and now each library has to implement all the different interfaces.

Doesn't that smell like there should be a `OsString` typeclass for common operations just like we have `Num`?

```haskell

class OsString a where
pathSeparator :: a
pathSeparators :: [a]
...
```