[Haskell-cafe] Pointless functors

[Conor McBride]

On 13 Mar 2009, at 14:32, Ross Paterson wrote:

> On Fri, Mar 13, 2009 at 03:18:15PM +0100, Martijn van Steenbergen  
> wrote:
>> Are there any functors f for which no point/pure/return :: a -> f a  
>> exists?
>
> No.  Choose an arbitrary element shape :: f () and define
>
>        point x = fmap (const x) shape

Correspondingly, consider the functor Const Void.

Cheers

Conor