[Haskell-cafe] bottomless Top?

[Jonathan Cast]

On 15 May 2008, at 4:29 AM, Conor McBride wrote:

> Replying slap-foreheadedly to own post...
>
> On 15 May 2008, at 11:56, Conor McBride wrote:
>
>> Folks
>>
>> I'm also wondering whether it makes sense to have a
>> "bottomless Top" type, with constructor _ and lazy pattern _
>> (with (undefined :: Top) equal to _). Then the constant-time
>> shape operator makes the same sort of sense as the
>> constant-time
>>
>>   inflate :: Functor f => f Zero -> f a
>
> We've got it already.
>
> data One
>
> would do, with smart constructor
>
> only :: One
> only = undefined

As I've mentioned before, my favorite data type

newtype One = One One

does the same, and stays in Haskell 98.  (And has the same weakness  
to seq: (`seq` ()) is perfectly strict (it's const undefined)).

jcc