[Haskell-cafe] There is no null; Maybe/Option types

[Henning Thielemann]

On Fri, 22 Apr 2011, Christopher Done wrote:

> Use of Fantom's save invoke and Maybe are more or less the same.
> 
> -- Hard way
> email = if userList /= Nothing
>            then let user = findUser "bob" (fromJust userList)
>                 in if user /= Nothing
>                       then getEmail (fromJust user)
>                       else Nothing
>            else Nothing

In idiomatic Haskell you would write

case userList of
    Nothing -> Nothing
    Just plainUserList =
       let user = findUser "bob" plainUserList
       ...

since (userList /= Nothing) requires an Eq instance without need and it 
requires fromJust. Or was there an educational purpose to write it with 
(/= Nothing) ?