[Haskell-cafe] Pointless functors

Ross Paterson ross at soi.city.ac.uk
Fri Mar 13 10:32:23 EDT 2009

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

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